build: issues with out-of-source (objdir=...)

Out-of-source build (objdir=/whatever) would be useful for doing bits with cvise so it can work in parallel.

With /tmp on tmpfs:

$ cd $(mktemp -d) && make -C /home/sam/git/dtrace-utils/ objdir=$(pwd) -j1
[...]
AR: libcommon.a
AR: libport.a
AR: libproc.a
SHLINK: libdtrace.so
SHLINK: libproc-dlmlib.so
cp: cannot create hard link 'test/triggers/libproc-dlmlib.so.0.0.0' to '/tmp/tmp.2aI49qXEfR/libproc-dlmlib.so.0.0.0': Invalid cross-device link
make: *** [Makerules:24: /tmp/tmp.2aI49qXEfR/libproc-dlmlib.so] Error 1
make: *** Deleting file '/tmp/tmp.2aI49qXEfR/libproc-dlmlib.so'

With both in /tmp:

$ cd $(mktemp -d) && make -C /tmp/dtrace-utils/ objdir=$(pwd) -j1
[...]
SHLINK: libdtrace.so
SHLINK: libproc-dlmlib.so
ln: failed to create symbolic link 'test/triggers/libproc-dlmlib.so.0': File exists
make: *** [Makerules:25: /tmp/tmp.Hu7sQqZzMN/libproc-dlmlib.so] Error 1
make: *** Deleting file '/tmp/tmp.Hu7sQqZzMN/libproc-dlmlib.so'

Also, it looks like configure does support --objdir but it also has a bunch of hardcoded build/. Not tried it.

Start by reading Makerules and configure, then inspect the hardcoded build/ paths mentioned in the issue. Reproduce the two out-of-source builds with objdir in separate temporary directories, including the cross-device and existing-symlink failures. Done means the reported builds complete successfully without those copy or symlink errors.