Add trivial check for stdatomic.h

cmake/system_check.cmake

@@ -116,3 +116,10 @@ set (CCOMMON_OPT "${CCOMMON_OPT} -DNO_AVX512")
 endif()
   file(REMOVE "avx512.c" "avx512.o")
 endif()
+
+include(CheckIncludeFile)
+CHECK_INCLUDE_FILE("stdatomic.h" HAVE_C11)
+if (HAVE_C11 EQUAL 1)
+message (STATUS found stdatomic.h)
+set (CCOMMON_OPT "${CCOMMON_OPT} -DHAVE_C11")
+endif()