All dependencies pulled from git should pass GIT_TAG to ExternalProject_Add()
pgmlink.cmake: Use specific commit, and use the same one for mac and linux.
Added cplex-shared.cmake, which creates shared libraries from pre-existing CPLEX static libraries.
cplex-shared.cmake: Use different linker flag for mac/linux
cplex-shared.cmake: Fixed linux targets.
Merge branch 'shared-cplex'