[OpenMP] Fix building the second import library when built in the main llvm build root

[mstorsjo]

Summary

Pass an absolute path to initial import library in this case, to
make it clear which file is intended. (For the generated build
files, cmake still uses relative paths as suitable.)

The issue was that the initial import library was stored in
ARCHIVE_OUTPUT_DIRECTORY as lib/libomp.dll.lib, while the same
file added as a source file to the second import library was
interpreted as runtime/src/libomp.dll.lib.

This is an alternative to D146894.

[vadikp-intel]

I will be good with this solution, but I think there could be a simpler one in the end. While CMAKE does wants to see a source, that does not have to be a cpp (which is what's causing this need to unnecessarily feed the first step's library to satisfy lib's attempt at def symbols resolution). There are other source types (e.g., a. txt) which will satisfy the source presence requirement but which CMAKE will filter out from the librarian generating the right command line for it.

I will submit a patch with this for review to https://reviews.llvm.org/D146894.

[mstorsjo]

In D146925#4225492, @vadikp-intel wrote:

I will be good with this solution, but I think there could be a simpler one in the end. While CMAKE does wants to see a source, that does not have to be a cpp (which is what's causing this need to unnecessarily feed the first step's library to satisfy lib's attempt at def symbols resolution). There are other source types (e.g., a. txt) which will satisfy the source presence requirement but which CMAKE will filter out from the librarian generating the right command line for it.

Oh, nice, if that works, that's probably even better!

I did try to convert the import library generation to a cmake custom target, and I got it working, but I'm not entirely convinced that it's any better than what we have right now.

[mstorsjo]

Superseded by the improved version of D146894.

openmp/runtime/src/CMakeLists.txt

else()
   get_target_property(LIBOMP_LIBRARY_DIR omp RUNTIME_OUTPUT_DIRECTORY)
 endif()
 if(NOT LIBOMP_LIBRARY_DIR)
   set(LIBOMP_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
   set(LIBOMP_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
 else()
   set(LIBOMP_LIBRARY_DIR ${LIBOMP_LIBRARY_DIR} PARENT_SCOPE)
 endif()
+get_target_property(LIBOMP_ARCHIVE_DIR omp ARCHIVE_OUTPUT_DIRECTORY)
+if(NOT LIBOMP_ARCHIVE_DIR)
+  set(LIBOMP_ARCHIVE_DIR ${CMAKE_CURRENT_BINARY_DIR})
+endif()
 set(LIBOMP_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
 
 # Add symbolic links to libomp
 if(NOT WIN32)
   add_custom_command(TARGET omp POST_BUILD
     COMMAND ${CMAKE_COMMAND} -E create_symlink ${LIBOMP_LIB_FILE}
       libgomp${LIBOMP_LIBRARY_SUFFIX}
     COMMAND ${CMAKE_COMMAND} -E create_symlink ${LIBOMP_LIB_FILE}
if(MSVC)
     add_custom_command(
       OUTPUT  ${LIBOMPIMP_GENERATED_DEF_FILE}
       COMMAND ${PERL_EXECUTABLE} ${LIBOMP_TOOLS_DIR}/generate-def.pl ${LIBOMP_GDFLAGS} -D NAME=${LIBOMP_LIB_FILE} -D NOORDINALS
           -o ${LIBOMPIMP_GENERATED_DEF_FILE} ${CMAKE_CURRENT_SOURCE_DIR}/dllexports
       DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/dllexports ${LIBOMP_TOOLS_DIR}/generate-def.pl
     )
     # while this is merely generating an import library off the one generated with the runtime dll,
     # kmp_global.cpp will satisfy the librarian's apparent ask to see the actual exported DATA items
-    set_source_files_properties(${LIBOMP_GENERATED_IMP_LIB_FILENAME} PROPERTIES GENERATED TRUE EXTERNAL_OBJECT TRUE)
-    add_library(${LIBOMP_IMP_LIB_TARGET} STATIC ${LIBOMP_GENERATED_IMP_LIB_FILENAME} kmp_global.cpp)
+    set_source_files_properties(${LIBOMP_ARCHIVE_DIR}/${LIBOMP_GENERATED_IMP_LIB_FILENAME} PROPERTIES GENERATED TRUE EXTERNAL_OBJECT TRUE)
+    add_library(${LIBOMP_IMP_LIB_TARGET} STATIC ${LIBOMP_ARCHIVE_DIR}/${LIBOMP_GENERATED_IMP_LIB_FILENAME} kmp_global.cpp)
     set_target_properties(${LIBOMP_IMP_LIB_TARGET} PROPERTIES
         PREFIX "" SUFFIX "" OUTPUT_NAME "${LIBOMP_IMP_LIB_FILE}" LINKER_LANGUAGE C
         STATIC_LIBRARY_OPTIONS "${CMAKE_LINK_DEF_FILE_FLAG}${CMAKE_CURRENT_BINARY_DIR}/${LIBOMPIMP_GENERATED_DEF_FILE}")
     add_dependencies(${LIBOMP_IMP_LIB_TARGET} omp libompimp-needed-def-file)
   endif()
 endif()
 
 # Building the Fortran module files