Merge branch 'C-features-Wundef' into release

Modules/Compiler/Clang-C-FeatureTests.cmake

@@ -1,9 +1,9 @@
 
 set(_cmake_oldestSupported "((__clang_major__ * 100) + __clang_minor__) >= 304")
 
-set(Clang_C11 "${_cmake_oldestSupported} && __STDC_VERSION__ >= 201112L")
+set(Clang_C11 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L")
 set(_cmake_feature_test_c_static_assert "${Clang_C11}")
-set(Clang_C99 "${_cmake_oldestSupported} && __STDC_VERSION__ >= 199901L")
+set(Clang_C99 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L")
 set(_cmake_feature_test_c_restrict "${Clang_C99}")
 set(_cmake_feature_test_c_variadic_macros "${Clang_C99}")
 

Modules/Compiler/GNU-C-FeatureTests.cmake

@@ -1,10 +1,10 @@
 
 set(_cmake_oldestSupported "(__GNUC__ * 100 + __GNUC_MINOR__) >= 407")
 
-set(GNU46_C11 "${_cmake_oldestSupported} && __STDC_VERSION__ >= 201112L")
+set(GNU46_C11 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L")
 set(_cmake_feature_test_c_static_assert "${GNU46_C11}")
 # Since 4.4 at least:
-set(GNU44_C99 "${_cmake_oldestSupported} && __STDC_VERSION__ >= 199901L")
+set(GNU44_C99 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L")
 set(_cmake_feature_test_c_restrict "${GNU44_C99}")
 set(_cmake_feature_test_c_variadic_macros "${GNU44_C99}")
 

Tests/Module/WriteCompilerDetectionHeader/CMakeLists.txt

@@ -63,6 +63,13 @@ if (CMAKE_CXX_COMPILER_ID STREQUAL GNU
   list(APPEND false_defs EXPECTED_COMPILER_CXX_VARIADIC_TEMPLATES)
 endif()
 
+if (CMAKE_C_COMPILER_ID STREQUAL GNU
+    OR CMAKE_C_COMPILER_ID STREQUAL Clang)
+  add_executable(C_undefined c_undefined.c)
+  set_property(TARGET C_undefined PROPERTY CXX_STANDARD 90)
+  target_compile_options(C_undefined PRIVATE -Werror=undef)
+endif()
+
 add_executable(WriteCompilerDetectionHeader main.cpp)
 set_property(TARGET WriteCompilerDetectionHeader PROPERTY CXX_STANDARD 98)
 set_defines(WriteCompilerDetectionHeader "${true_defs}" "${false_defs}")

Tests/Module/WriteCompilerDetectionHeader/c_undefined.c

@@ -0,0 +1,7 @@
+
+#include "test_compiler_detection.h"
+
+int main()
+{
+  return 0;
+}