Adding MPI decls for external GPTL

When external GPTL library is used (GPTL_PATH is set to point to
an external GPTL library build), not all declarations required by
GPTL is exported. Adding declaration to indicate if MPI is
available (required by the GPTL header files) to correctly use
the GPTL header files.

Without this change the build fails with Intel/GNU compilers since
the default (incorrect) function declarations in GPTL headers are
used during the build.

Author: jayeshkrishna

src/clib/CMakeLists.txt

@@ -68,6 +68,11 @@ if (PIO_ENABLE_TIMING)
       PUBLIC ${GPTL_C_INCLUDE_DIRS})
     target_link_libraries (pioc
       PUBLIC ${GPTL_C_LIBRARIES})
+
+    # GPTL expects HAVE_MPI, if MPI is available, when using GPTL header files
+    if (NOT PIO_USE_MPISERIAL)
+      target_compile_definitions (pioc PUBLIC HAVE_MPI)
+    endif ()
   else ()
     message (STATUS "Using internal GPTL C library for timing")
     target_include_directories (pioc