[openmp][cmake] Add 'append' cmake command if it's not already there

Author: aganea

openmp/cmake/HandleOpenMPOptions.cmake

@@ -9,6 +9,14 @@ if (NOT COMMAND append_if)
   endfunction()
 endif()
 
+if (NOT COMMAND append)
+  function(append value)
+    foreach(variable ${ARGN})
+      set(${variable} "${${variable}} ${value}" PARENT_SCOPE)
+    endforeach(variable)
+  endfunction()
+endif()
+
 # MSVC and clang-cl in compatibility mode map -Wall to -Weverything.
 # TODO: LLVM adds /W4 instead, check if that works for the OpenMP runtimes.
 if (NOT MSVC)
@@ -44,9 +52,9 @@ append_if(OPENMP_HAVE_DATA_SECTIONS "-fdata-sections" CMAKE_C_FLAGS CMAKE_CXX_FL
 
 if (MSVC)
   # Disable "warning C4201: nonstandard extension used: nameless struct/union"
-  append_if(TRUE "-wd4201" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append("-wd4201" CMAKE_C_FLAGS CMAKE_CXX_FLAGS )
 
   # Disable "warning C4190: '__kmpc_atomic_cmplx8_rd' has C-linkage specified, but returns
   # UDT '__kmp_cmplx64_t' which is incompatible with C"
-  append_if(TRUE "-wd4190" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+  append("-wd4190" CMAKE_C_FLAGS CMAKE_CXX_FLAGS )
 endif()