Merge branch 'xl-cc-default-std' into release-3.11

Merge-request: !1854

Modules/CMakeCCompilerId.c.in

@@ -34,7 +34,8 @@ char const *info_cray = "INFO" ":" "compiler_wrapper[CrayPrgEnv]";
 @CMAKE_C_COMPILER_ID_ERROR_FOR_TEST@
 
 #if !defined(__STDC__)
-# if defined(_MSC_VER) && !defined(__clang__)
+# if (defined(_MSC_VER) && !defined(__clang__)) \
+  || (defined(__ibmxl__) || defined(__IBMC__))
 #  define C_DIALECT "90"
 # else
 #  define C_DIALECT