[openmp] - Rework openmp-config for portability (llvm#2857)

Do not depend on CMAKE_INSTALL_PREFIX as the final location can be
different.

Author: estewart08

openmp/CMakeLists.txt

@@ -68,6 +68,8 @@ else()
     set(OPENMP_INSTALL_LIBDIR "lib${LLVM_LIBDIR_SUFFIX}" CACHE STRING
         "Path where built OpenMP libraries should be installed.")
   endif()
+  set(OPENMP_INSTALL_CFGDIR "lib/cmake" CACHE STRING
+        "Path where OpenMP config should be installed")
 
   if (NOT MSVC)
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)
@@ -123,6 +125,8 @@ if (OPENMP_STANDALONE_BUILD)
     set(OPENMP_LIBDIR_SUFFIX "/asan")
     set(OPENMP_INSTALL_LIBDIR "lib${OPENMP_LIBDIR_SUFFIX}")
   endif()
+  set(OPENMP_INSTALL_CFGDIR "${OPENMP_INSTALL_LIBDIR}/cmake" CACHE STRING
+        "Path where OpenMP config should be installed")
 endif()
 
 # Check and set up common compiler flags.

openmp/runtime/openmp-config.cmake.in

@@ -1,12 +1,9 @@
 @PACKAGE_INIT@
-get_filename_component(openmp_PACKAGE_PREFIX_DIR "${PACKAGE_PREFIX_DIR}" REALPATH)
 
+# Partial path copied from build variable OPENMP_INSTALL_LIBDIR
 set( openmp_LIB_DIR "@OPENMP_INSTALL_LIBDIR@" )
-set_and_check( openmp_LIB_INSTALL_DIR "@CMAKE_INSTALL_PREFIX@/@OPENMP_INSTALL_LIBDIR@" )
-set_and_check( openmp_LIB_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@")
-
-string(REPLACE "${openmp_PACKAGE_PREFIX_DIR}/" "" openmp_LIB_NO_PACKAGE_PREFIX_PATH_TEMP ${openmp_LIB_INSTALL_DIR})
-set(openmp_LIB_NO_PACKAGE_PREFIX_PATH ${openmp_LIB_NO_PACKAGE_PREFIX_PATH_TEMP})
 
+# Full path to libomp.so using OPENMP_INSTALL_PREFIX and OPENMP_INSTALL_LIBDIR partial path.
+set_and_check( openmp_LIB_INSTALL_DIR "${PACKAGE_PREFIX_DIR}/@OPENMP_INSTALL_LIBDIR@" )
 
 include( "${CMAKE_CURRENT_LIST_DIR}/openmpTargets.cmake" )

openmp/runtime/src/CMakeLists.txt

@@ -463,17 +463,19 @@ else()
     install(TARGETS omp ${export_to_llvmexports} EXPORT openmpTargets ${LIBOMP_INSTALL_KIND}
             DESTINATION "${OPENMP_INSTALL_LIBDIR}")
     install(EXPORT openmpTargets FILE openmpTargets.cmake NAMESPACE OpenMP::
-            DESTINATION ${OPENMP_INSTALL_LIBDIR}/cmake/openmp)
+            DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp)
   endif()
+
   # Create cmake configuration files
   include(CMakePackageConfigHelpers)
 
   configure_package_config_file(
    ../openmp-config.cmake.in
    openmp-config.cmake
-   INSTALL_DESTINATION ${OPENMP_INSTALL_LIBDIR}/cmake/openmp )
+   INSTALL_DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp )
+
   install(FILES ${CMAKE_CURRENT_BINARY_DIR}/openmp-config.cmake
-          DESTINATION ${OPENMP_INSTALL_LIBDIR}/cmake/openmp )
+          DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp)
 
   if(${LIBOMP_INSTALL_ALIASES})
     # Create aliases (symlinks) of the library for backwards compatibility