[openmp] [cmake] Make libgomp & libiomp5 alias install optional

[mgorny]

Summary

Introduce a new LIBOMP_INSTALL_VARIABLES cache variable that can be used to disable creating libgomp and libiomp5 aliases on 'make install'. Those aliases are undesired e.g. on Gentoo systems where libomp is used purely by clang.

[jlpeyton]

LGTM.

[mgorny]

Thanks for the review, committed now.

runtime/CMakeLists.txt

 else()
   set(LIBOMP_LIBRARY_SUFFIX ${CMAKE_STATIC_LIBRARY_SUFFIX})
   set(LIBOMP_LIBRARY_KIND STATIC)
   set(LIBOMP_INSTALL_KIND ARCHIVE)
 endif()
 
 set(LIBOMP_LIB_FILE ${LIBOMP_LIB_NAME}${LIBOMP_LIBRARY_SUFFIX})
 
+# Optional backwards compatibility aliases.
+set(LIBOMP_INSTALL_ALIASES TRUE CACHE BOOL
+  "Install libgomp and libiomp5 library aliases for backwards compatibility")
+
 # Print configuration after all variables are set.
 if(${LIBOMP_STANDALONE_BUILD})
   libomp_say("Operating System     -- ${CMAKE_SYSTEM_NAME}")
   libomp_say("Target Architecture  -- ${LIBOMP_ARCH}")
   if(${MIC})
     libomp_say("Intel(R) MIC Architecture    -- ${LIBOMP_MIC_ARCH}")
   endif()
   libomp_say("Build Type           -- ${CMAKE_BUILD_TYPE}")

runtime/src/CMakeLists.txt

install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E copy \"${LIBOMP_LIB_FILE}\"
       \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY \${CMAKE_INSTALL_PREFIX}/bin)")
     install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E copy \"${LIBOMP_IMP_LIB_FILE}\"
       \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY \${CMAKE_INSTALL_PREFIX}/lib${LIBOMP_LIBDIR_SUFFIX})")
   endforeach()
 else()
 
   install(TARGETS omp ${LIBOMP_INSTALL_KIND} DESTINATION lib${LIBOMP_LIBDIR_SUFFIX})
 
+  if(${LIBOMP_INSTALL_ALIASES})
     # Create aliases (symlinks) of the library for backwards compatibility
     set(LIBOMP_ALIASES "libgomp;libiomp5")
     foreach(alias IN LISTS LIBOMP_ALIASES)
       install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E create_symlink \"${LIBOMP_LIB_FILE}\"
         \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY
         \$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/lib${LIBOMP_LIBDIR_SUFFIX})")
     endforeach()
   endif()
+endif()
 install(
   FILES
   ${CMAKE_CURRENT_BINARY_DIR}/omp.h
   DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH}
 )
 if(${LIBOMP_OMPT_SUPPORT})
   install(FILES ${CMAKE_CURRENT_BINARY_DIR}/ompt.h DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH})
 endif()