In the CMake build system, use CMAKE_SHARED_LIBRARY_CXX_FLAGS to get the PIC compiler flag instead of the hardcoded '-fPIC' value.
In the CMake build system, use CMAKE_SHARED_LIBRARY_CXX_FLAGS to
get the PIC compiler flag instead of the hardcoded '-fPIC' value.

Suggested by: @cwsmith

mfem/mfem,mfem/mfem,mfem/mfem,mfem/mfem,mfem/mfem