[OpenMP] Create versioned libgomp softlinks (llvm#112973)

Add libgomp.1.dylib for MacOS and libgomp.so.1 for Linux

Linkers on Mac and Linux pick up versioned libgomp dynamic library
files. The existing softlinks (libgomp.dylib for MacOS and libgomp.so
for Linux) are insufficient. This helps alleviate the issue of mixing
libgomp and libomp at runtime.

openmp/runtime/src/CMakeLists.txt

@@ -253,6 +253,17 @@ if(NOT WIN32)
       libiomp5${LIBOMP_LIBRARY_SUFFIX}
     WORKING_DIRECTORY ${LIBOMP_LIBRARY_DIR}
   )
+  if(LIBOMP_ENABLE_SHARED)
+    if(APPLE)
+      set(VERSIONED_LIBGOMP_NAME libgomp.1${LIBOMP_LIBRARY_SUFFIX})
+    else()
+      set(VERSIONED_LIBGOMP_NAME libgomp${LIBOMP_LIBRARY_SUFFIX}.1)
+    endif()
+    add_custom_command(TARGET omp POST_BUILD
+      COMMAND ${CMAKE_COMMAND} -E create_symlink ${LIBOMP_LIB_FILE} ${VERSIONED_LIBGOMP_NAME}
+      WORKING_DIRECTORY ${LIBOMP_LIBRARY_DIR}
+    )
+  endif()
 endif()
 
 # Definitions for testing, for reuse when testing libomptarget-nvptx.
@@ -439,13 +450,18 @@ else()
 
   if(${LIBOMP_INSTALL_ALIASES})
     # Create aliases (symlinks) of the library for backwards compatibility
+    extend_path(outdir "${CMAKE_INSTALL_PREFIX}" "${OPENMP_INSTALL_LIBDIR}")
     set(LIBOMP_ALIASES "libgomp;libiomp5")
     foreach(alias IN LISTS LIBOMP_ALIASES)
-      extend_path(outdir "${CMAKE_INSTALL_PREFIX}" "${OPENMP_INSTALL_LIBDIR}")
       install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E create_symlink \"${LIBOMP_LIB_FILE}\"
         \"${alias}${LIBOMP_LIBRARY_SUFFIX}\" WORKING_DIRECTORY
         \"\$ENV{DESTDIR}${outdir}\")")
     endforeach()
+    if(LIBOMP_ENABLE_SHARED)
+      install(CODE "execute_process(COMMAND \"\${CMAKE_COMMAND}\" -E create_symlink \"${LIBOMP_LIB_FILE}\"
+        \"${VERSIONED_LIBGOMP_NAME}\" WORKING_DIRECTORY
+        \"\$ENV{DESTDIR}${outdir}\")")
+    endif()
   endif()
 endif()
 install(