[Libomp] Place generated OpenMP headers into build resource directory

Summary:
These headers are a part of the compiler's resource directory once
installed. However, they are currently placed in the binary directory
temporarily. This makes it more difficult to use the compiler out of the
build directory and will cause issues when moving to `liboffload`. This
patch changes the logic to write these instead to the copmiler's
resource directory inside of the build tree.

NOTE: This doesn't change the Fortran headers, I don't know enough about
those and it won't use the same directory.

Author: jhuber6

openmp/runtime/src/CMakeLists.txt

@@ -10,12 +10,19 @@
 
 include(ExtendPath)
 
+# The generated headers will be placed in clang's resource directory if present.
+if(${OPENMP_STANDALONE_BUILD})
+  set(LIBOMP_HEADERS_INTDIR ${CMAKE_CURRENT_BINARY_DIR})
+else()
+  set(LIBOMP_HEADERS_INTDIR ${LLVM_BINARY_DIR}/${LIBOMP_HEADERS_INSTALL_PATH})
+endif()
+
 # Configure omp.h, kmp_config.h and omp-tools.h if necessary
-configure_file(${LIBOMP_INC_DIR}/omp.h.var omp.h @ONLY)
-configure_file(${LIBOMP_INC_DIR}/ompx.h.var ompx.h @ONLY)
-configure_file(kmp_config.h.cmake kmp_config.h @ONLY)
+configure_file(${LIBOMP_INC_DIR}/omp.h.var ${LIBOMP_HEADERS_INTDIR}/omp.h @ONLY)
+configure_file(${LIBOMP_INC_DIR}/ompx.h.var ${LIBOMP_HEADERS_INTDIR}/ompx.h @ONLY)
+configure_file(kmp_config.h.cmake ${LIBOMP_HEADERS_INTDIR}/kmp_config.h @ONLY)
 if(${LIBOMP_OMPT_SUPPORT})
-  configure_file(${LIBOMP_INC_DIR}/omp-tools.h.var omp-tools.h @ONLY)
+  configure_file(${LIBOMP_INC_DIR}/omp-tools.h.var ${LIBOMP_HEADERS_INTDIR}/omp-tools.h @ONLY)
 endif()
 
 # Generate message catalog files: kmp_i18n_id.inc and kmp_i18n_default.inc
@@ -419,15 +426,15 @@ else()
 endif()
 install(
   FILES
-  ${CMAKE_CURRENT_BINARY_DIR}/omp.h
-  ${CMAKE_CURRENT_BINARY_DIR}/ompx.h
+  ${LIBOMP_HEADERS_INTDIR}/omp.h
+  ${LIBOMP_HEADERS_INTDIR}/ompx.h
   DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH}
 )
 if(${LIBOMP_OMPT_SUPPORT})
-  install(FILES ${CMAKE_CURRENT_BINARY_DIR}/omp-tools.h DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH})
+  install(FILES ${LIBOMP_HEADERS_INTDIR}/omp-tools.h DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH})
   # install under legacy name ompt.h
-  install(FILES ${CMAKE_CURRENT_BINARY_DIR}/omp-tools.h DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH} RENAME ompt.h)
-  set(LIBOMP_OMP_TOOLS_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR} PARENT_SCOPE)
+  install(FILES ${LIBOMP_HEADERS_INTDIR}/omp-tools.h DESTINATION ${LIBOMP_HEADERS_INSTALL_PATH} RENAME ompt.h)
+  set(LIBOMP_OMP_TOOLS_INCLUDE_DIR ${LIBOMP_HEADERS_INTDIR} PARENT_SCOPE)
 endif()
 if(${BUILD_FORTRAN_MODULES})
   set (destination ${LIBOMP_HEADERS_INSTALL_PATH})