[openmp] - Add openmp_INCLUDE_DIR to openmp-config.cmake (llvm#2972)

Utilize PATH_VARS to generate config variables.
Add interface_include_directories to OpenMP::omp target.

Author: estewart08

openmp/runtime/openmp-config.cmake.in

@@ -3,7 +3,11 @@
 # Partial path copied from build variable OPENMP_INSTALL_LIBDIR
 set( openmp_LIB_DIR "@OPENMP_INSTALL_LIBDIR@" )
 
-# Full path to libomp.so using OPENMP_INSTALL_PREFIX and OPENMP_INSTALL_LIBDIR partial path.
-set_and_check( openmp_LIB_INSTALL_DIR "${PACKAGE_PREFIX_DIR}/@OPENMP_INSTALL_LIBDIR@" )
+# Full path to libomp.so using PACKAGE_PREFIX_DIR and OPENMP_INSTALL_LIBDIR partial path.
+set_and_check( openmp_LIB_INSTALL_DIR "@PACKAGE_OPENMP_INSTALL_LIBDIR@" )
+
+# Full path to omp.h using PACKAGE_PREFIX and LIBOMP_HEADERS_INSTALL_PATH partial path.
+set_and_check( openmp_INCLUDE_DIR "@PACKAGE_LIBOMP_HEADERS_INSTALL_PATH@" )
+set_and_check( openmp_INCLUDE_DIRS "${openmp_INCLUDE_DIR}" )
 
 include( "${CMAKE_CURRENT_LIST_DIR}/openmpTargets.cmake" )

openmp/runtime/src/CMakeLists.txt

@@ -464,6 +464,7 @@ else()
             DESTINATION "${OPENMP_INSTALL_LIBDIR}")
     install(EXPORT openmpTargets FILE openmpTargets.cmake NAMESPACE OpenMP::
             DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp)
+    target_include_directories(omp PUBLIC $<INSTALL_INTERFACE:${LIBOMP_HEADERS_INSTALL_PATH}>)
   endif()
 
   # Create cmake configuration files
@@ -472,7 +473,8 @@ else()
   configure_package_config_file(
    ../openmp-config.cmake.in
    openmp-config.cmake
-   INSTALL_DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp )
+   INSTALL_DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp
+   PATH_VARS LIBOMP_HEADERS_INSTALL_PATH OPENMP_INSTALL_LIBDIR)
 
   install(FILES ${CMAKE_CURRENT_BINARY_DIR}/openmp-config.cmake
           DESTINATION ${OPENMP_INSTALL_CFGDIR}/openmp)