Features: Fix C90 feature detection.

This bug caused c_function_prototypes to not be recorded at configure
time when compiling with -std=gnu99 or similar. In the case of feature
recording, that was not a problem, because the logic in
CMakeDetermineCompileFeatures.cmake currently assumes that a feature
present for an earlier standard is present for a later standard.

However, the detection strings are also used in WriteCompilerDetectionHeader,
so the feature macro has been defined to '0' when using a later language
dialect.

Fix that by not checking the existence of the __STDC_VERSION__ macro at
all when detecting C90 features.

1 files changed, 29 insertions, 0 deletions

diff --git a/Tests/Module/WriteCompilerDetectionHeader/main_multi.c b/Tests/Module/WriteCompilerDetectionHeader/main_multi.c
new file mode 100644
index 0000000..6f4573f
--- /dev/null
+++ b/Tests/Module/WriteCompilerDetectionHeader/main_multi.c
@@ -0,0 +1,29 @@
+
+#include "multi_file_compiler_detection.h"
+
+#if !defined(MULTI_COMPILER_C_FUNCTION_PROTOTYPES) || !MULTI_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected MULTI_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#  error Expected EXPECTED_COMPILER_C_FUNCTION_PROTOTYPES
+#endif
+
+#if !defined(MULTI_COMPILER_C_RESTRICT) || !MULTI_COMPILER_C_RESTRICT
+#  if EXPECTED_COMPILER_C_RESTRICT
+#    error Expected MULTI_COMPILER_C_RESTRICT
+#  endif
+#else
+#  if !EXPECTED_COMPILER_C_RESTRICT
+#    error Expect no MULTI_COMPILER_C_RESTRICT
+#  endif
+#endif
+
+#ifdef MULTI_COMPILER_CXX_STATIC_ASSERT
+#error Expect no CXX features defined
+#endif
+
+int main()
+{
+  return 0;
+}