Merge Pull Request trilinos#9092 from bartlettroscoe/Trilinos/8449-at…

…dm-compiler-flags-fix

Automatically Merged using Trilinos Pull Request AutoTester
PR Title: Set non-cache vars for CMAKE_<LANG>_FLAGS with user override (trilinos#8449)
PR Author: bartlettroscoe

cmake/std/atdm/ATDMDevEnvSettings.cmake

@@ -222,16 +222,12 @@ IF (ATDM_FPIC)
   SET(CMAKE_POSITION_INDEPENDENT_CODE ON CACHE BOOL "Build targets with position independent code")
 ENDIF()
 
-ATDM_SET_CACHE(CMAKE_C_FLAGS
-  "$ENV{ATDM_CONFIG_C_FLAGS} $ENV{EXTRA_C_FLAGS}" CACHE STRING)
-ATDM_SET_CACHE(CMAKE_CXX_FLAGS
-  "$ENV{ATDM_CONFIG_CXX_FLAGS}${EXTRA_EXTRA_CXX_FLAGS} $ENV{EXTRA_CXX_FLAGS}" CACHE STRING)
-ATDM_SET_CACHE(CMAKE_Fortran_FLAGS
-  "$ENV{ATDM_CONFIG_Fortran_FLAGS} $ENV{EXTRA_Fortran_FLAGS}" CACHE STRING)
-# NOTE: That above "EXTRA_<LANG>_FLAGS" env vars are left in for backward
-# compatibility with the EMPIRE configuration and are not directly set in any
-# offical ATDM Trilinos configuration setup.  Only the
-# "ATDM_CONFIG_<LANG>_FLAGS" env vars are set.
+SET(CMAKE_C_FLAGS
+  "$ENV{ATDM_CONFIG_C_FLAGS} ${CMAKE_C_FLAGS}")
+SET(CMAKE_CXX_FLAGS
+  "$ENV{ATDM_CONFIG_CXX_FLAGS} ${EXTRA_EXTRA_CXX_FLAGS} ${CMAKE_CXX_FLAGS}")
+SET(CMAKE_Fortran_FLAGS
+  "$ENV{ATDM_CONFIG_Fortran_FLAGS} ${CMAKE_Fortran_FLAGS}")
 
 IF (NOT "$ENV{ATDM_CONFIG_OPENMP_FORTRAN_FLAGS}" STREQUAL "")
   ATDM_SET_CACHE(OpenMP_Fortran_FLAGS "$ENV{ATDM_CONFIG_OPENMP_FORTRAN_FLAGS}"

cmake/std/atdm/README.md

@@ -14,6 +14,7 @@ build locally as described below.
 
 **Outline:**
 * <a href="#quick-start">Quick-start</a>
+* <a href="#setting-and-overridding-compiler-flags">Setting and overridding compiler flags</a>
 * <a href="#parallel-build-and-test-processes">Parallel build and test processes</a>
 * <a href="#installation-and-usage">Installation and usage</a>
 * <a href="#checkin-test-atdmsh">checkin-test-atdm.sh</a>
@@ -414,6 +415,21 @@ where if the CMake cache variable `ATDM_INSTALLED_ENV_LOAD_SCRIPT_NAME` is not
 specified, then it is given the name `load_matching_env.sh` by default.
 
 
+## Setting and overridding compiler flags
+
+Any selected configuration may set C, C++, and Fortran compiler flags by
+internally setting the variables `CMAKE_C_FLAGS`, `CMAKE_CXX_FLAGS`, and
+`CMAKE_Fortran_FLAGS`.  However, the user can also append (and therefore
+override) any of these compiler flags by configuring with the standard CMake
+cache variables:
+
+```
+  -D CMAKE_C_FLAGS="<extra_c_flags>"
+  -D CMAKE_CXX_FLAGS="<extra_cxx_flags>"
+  -D CMAKE_Fortran_FLAGS="<extra_fortran_flags>"
+```
+
+
 ## Parallel build and test processes
 
 By default, each system's `<system_name>/environment.sh` script automatically