Hardcoded lib64 directory in libgeant321.so linker line fails on debian systems

The line `SET(DEPENDENCIES eicbase ayk qfield tracking ${G3VMC}/lib64/libgeant321.so)` (https://github.com/eic/EicRoot/blob/3c0bab0dc4eca7f92c8aa9c49ecfe40620d4f80c/eic/htc/CMakeLists.txt#L41) in (only) htc fails to link on debian systems. On those systems, the standard location is `${G3VMC}/lib/libgeant321.so`

I suspect a solution can be implemented with [find_library](https://cmake.org/cmake/help/latest/command/find_library.html), e.g.
```cmake
FIND_LIBRARY(LIBGEANT321 libgeant321.so PATHS ${G3VMC})
SET(DEPENDENCIES eicbase ayk qfield tracking ${LIBGEANT321})
```
but this is untested.

Here is the following error:
```
1426 [ 96%] Building CXX object eic/htc/CMakeFiles/htc.dir/TrKalmanNode.cxx.o
1427 cd /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build/eic/htc && /cvmfs/eic.opensciencegrid.org/packages/spack/rollout/lib/spack/env/gcc/g++ -Dhtc_EXPORTS -I/cvmfs/eic.openscien
cegrid.org/packages/root/6.18.04/linux-ubuntu18.04-x86_64-gcc-9.3.0-eryzq56pj6y47spiuqpoozuzzwcojujd/include -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/fairtools -I/tmp/e
icbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/geobase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/parbase -I/tmp/eicbld/spack-sta
ge/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase -I/tmp/eicbld/spack-stage/spack-stage-eicro
ot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbInterface -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbValidation -I/tmp/eicbld/spack-stage/spack-stage
-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbUtils -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-ma
ster-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/ayk -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6se
lgn6u2mnn26pm5qor2as2pi/spack-src/eic/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/tracking -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mn
n26pm5qor2as2pi/spack-src/eic/htc -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/trackbase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2
pi/spack-src/pnddata -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/pnddata/TrackData -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/sp
ack-src/PndTools/generalTools -g -Wall -Wno-deprecated-declarations -Wno-parentheses -Wno-comment -Wno-unused -Wno-sign-compare -Wno-reorder -Wno-format -std=c++11 -Wno-narrowing -Wno-address -pthread -fPIC -O2 -g -DNDEBUG
-fPIC -std=gnu++11 -o CMakeFiles/htc.dir/TrKalmanNode.cxx.o -c /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/htc/TrKalmanNode.cxx
1428 [ 96%] Building CXX object eic/htc/CMakeFiles/htc.dir/TrKalmanNodeLocation.cxx.o
1429 cd /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build/eic/htc && /cvmfs/eic.opensciencegrid.org/packages/spack/rollout/lib/spack/env/gcc/g++ -Dhtc_EXPORTS -I/cvmfs/eic.openscien
cegrid.org/packages/root/6.18.04/linux-ubuntu18.04-x86_64-gcc-9.3.0-eryzq56pj6y47spiuqpoozuzzwcojujd/include -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/fairtools -I/tmp/e
icbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/geobase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/parbase -I/tmp/eicbld/spack-sta
ge/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase -I/tmp/eicbld/spack-stage/spack-stage-eicro
ot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbInterface -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbValidation -I/tmp/eicbld/spack-stage/spack-stage
-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbUtils -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-ma
ster-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/ayk -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6se
lgn6u2mnn26pm5qor2as2pi/spack-src/eic/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/tracking -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mn
n26pm5qor2as2pi/spack-src/eic/htc -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/trackbase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2
pi/spack-src/pnddata -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/pnddata/TrackData -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/sp
ack-src/PndTools/generalTools -g -Wall -Wno-deprecated-declarations -Wno-parentheses -Wno-comment -Wno-unused -Wno-sign-compare -Wno-reorder -Wno-format -std=c++11 -Wno-narrowing -Wno-address -pthread -fPIC -O2 -g -DNDEBUG
-fPIC -std=gnu++11 -o CMakeFiles/htc.dir/TrKalmanNodeLocation.cxx.o -c /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/htc/TrKalmanNodeLocation.cxx
1430 [ 96%] Building CXX object eic/htc/CMakeFiles/htc.dir/G__htc.cxx.o
1431 cd /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build/eic/htc && /cvmfs/eic.opensciencegrid.org/packages/spack/rollout/lib/spack/env/gcc/g++ -Dhtc_EXPORTS -I/cvmfs/eic.openscien
cegrid.org/packages/root/6.18.04/linux-ubuntu18.04-x86_64-gcc-9.3.0-eryzq56pj6y47spiuqpoozuzzwcojujd/include -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/fairtools -I/tmp/e
icbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/geobase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/parbase -I/tmp/eicbld/spack-sta
ge/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase -I/tmp/eicbld/spack-stage/spack-stage-eicro
ot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbInterface -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbValidation -I/tmp/eicbld/spack-stage/spack-stage
-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/dbase/dbUtils -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-ma
ster-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/ayk -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/base -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6se
lgn6u2mnn26pm5qor2as2pi/spack-src/eic/field -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/eic/tracking -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mn
n26pm5qor2as2pi/spack-src/eic/htc -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/trackbase -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2
pi/spack-src/pnddata -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-src/pnddata/TrackData -I/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/sp
ack-src/PndTools/generalTools -g -Wall -Wno-deprecated-declarations -Wno-parentheses -Wno-comment -Wno-unused -Wno-sign-compare -Wno-reorder -Wno-format -std=c++11 -Wno-narrowing -Wno-address -pthread -fPIC -O2 -g -DNDEBUG
-fPIC -std=gnu++11 -o CMakeFiles/htc.dir/G__htc.cxx.o -c /tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build/eic/htc/G__htc.cxx
>> 1432 make[2]: *** No rule to make target '/cvmfs/eic.opensciencegrid.org/packages/geant3-vmc/3-4/linux-ubuntu18.04-x86_64-gcc-9.3.0-sfzvzntzxd5k6yorkyrbn26mkmvz5pxm/lib64/libgeant321.so', needed by 'eic/htc/libhtc.so'. Stop.
1433 make[2]: Leaving directory '/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build'
1434 CMakeFiles/Makefile2:3011: recipe for target 'eic/htc/CMakeFiles/htc.dir/all' failed
>> 1435 make[1]: *** [eic/htc/CMakeFiles/htc.dir/all] Error 2
1436 make[1]: Leaving directory '/tmp/eicbld/spack-stage/spack-stage-eicroot-master-d756md6selgn6u2mnn26pm5qor2as2pi/spack-build'
1437 Makefile:152: recipe for target 'all' failed
>> 1438 make: *** [all] Error 2
```