Removing -I/usr/include in Android build

Hi, I'm trying to compile Boost for Android, this is the code that I'm using.

```
./bootstrap.sh -with-toolset=gcc

userConfigs=$srcdir/$_srcname/user-config.jam

cat << EOF > "${userConfigs}"
using clang : android : ${ANDROID_CXX} :
${ANDROID_AR} \
${ANDROID_AS}
;
EOF

./b2 install \
--prefix="$srcdir/fakeinstall" \
--user-config="${userConfigs}" \
--layout=system \
--with-atomic \
--with-chrono \
--with-container \
--with-date_time \
--with-exception \
--with-fiber \
--with-filesystem \
--with-graph \
--with-graph_parallel \
--with-iostreams \
--with-locale \
--with-log \
--with-math \
--with-mpi \
--with-program_options \
--with-random \
--with-regex \
--with-serialization \
--with-system \
--with-test \
--with-thread \
--with-timer \
--with-type_erasure \
--with-wave \
--with-stacktrace \
-sICONV_PATH="${ANDROID_PREFIX}" \
variant=release \
debug-symbols=off \
runtime-link=shared \
link=shared,static \
target-os=android \
toolset=clang-android \
architecture=arm \
threading=multi \
address-model=64 \
cflags="-I${ANDROIND_PREFIX_INCLUDE}" \
cxxflags="-I${ANDROIND_PREFIX_INCLUDE}" \
linkflags="-L${ANDROIND_PREFIX_LIB}"
```

The build fails and this command popup (over many other error messages).

```
"/opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android24-clang++" -I/opt/android-libs/aarch64/include -DBOOST_ALL_NO_LIB=1 -DBOOST_COBALT_USE_STD_PMR=1 -DBOOST_MPI_DYN_LINK=1 -DBOOST_MPI_SOURCE=1 -DNDEBUG -I"." -I"/usr/include" -c -o "bin.v2/libs/mpi/build/clang-linux-android/release/local-visibility-global/target-os-android/threading-multi/visibility-hidden/cartesian_communicator.o" "libs/mpi/src/cartesian_communicator.cpp"
```

With this error message:

```
In file included from libs/mpi/src/cartesian_communicator.cpp:9:
In file included from /opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/algorithm:1710:
In file included from /opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/type_traits:538:
/opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/../sysroot/usr/include/c++/v1/cstdint:149:5: error: tried including but didn't find libc++'s header. This usually means that your header search paths are not configured properly. The header search paths should contain the C++ Standard Library headers before any C Standard Library, and you are probably using compiler flags that make that not be the case.
# error tried including but didn't find libc++'s header. \
^
```

And have found that removing the ```-I"/usr/include"``` flag and executing that command directly it compiles fine.
The problem is that I have not found where that flag was introduced.
Did tried grepping for _-I.*/include_ and _/usr/include_ and other similar expressions but did not found any meaningful result.
I'm trying to compile Boost 1.84.0.