Use OPENMP_USER_PATH to set OpenMP_<lang>_INCLUDE_DIR

- This appears to direct CMAKE's find_package (OpenMP)
  to detect a non-system installation

Author: dengwirda

src/CMakeLists.txt

@@ -4,9 +4,15 @@ function (cfg_compile_options OPT CFG)
 endfunction ()
 
 include (CheckCXXCompilerFlag)
+include (CheckIPOSupported)
 
 set (CMAKE_CXX_STANDARD 17)
-set (CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+
+check_ipo_supported (RESULT IPO OUTPUT IPO_ERR LANGUAGES C CXX)
+
+if (IPO)
+  set (CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+endif ()
 
 if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU"   OR
     CMAKE_CXX_COMPILER_ID STREQUAL "Clang" OR
@@ -78,8 +84,9 @@ endif ()
 
 if (DEFINED OPENMP_USER_PATH)
   message (STATUS "Testing user OpenMP path")
-  find_package (OpenMP 
-                PATHS ${OPENMP_USER_PATH} NO_DEFAULT_PATH)
+  set (  OpenMP_C_INCLUDE_DIR ${OPENMP_USER_PATH})
+  set (OpenMP_CXX_INCLUDE_DIR ${OPENMP_USER_PATH})
+  find_package (OpenMP)
 else ()
   find_package (OpenMP)
 endif ()
@@ -92,6 +99,7 @@ endif ()
 if (OpenMP_CXX_FOUND)
   message (STATUS "OpenMP library found")
   message (STATUS "OpenMP inc. lib: ${OpenMP_CXX_LIB_NAMES}")
+  message (STATUS "OpenMP inc. lib: ${OpenMP_CXX_LIBRARIES}")
 else ()
   message (STATUS "OpenMP library not found")
 endif ()