Features: Fix references to CXX compiler version in Clang-C.cmake.

Modules/Compiler/Clang-C.cmake

@@ -6,7 +6,7 @@ if(WIN32 OR (APPLE AND NOT appleClangPolicy STREQUAL NEW))
   return()
 endif()
 
-if(NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.4)
+if(NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 3.4)
   set(CMAKE_C90_STANDARD_COMPILE_OPTION "-std=c90")
   set(CMAKE_C90_EXTENSION_COMPILE_OPTION "-std=gnu90")
 
@@ -24,7 +24,7 @@ macro(cmake_record_c_compile_features)
     record_compiler_features(C "-std=${std_version}" ${list})
   endmacro()
 
-  if (UNIX AND NOT CMAKE_CXX_COMPILER_VERSION VERSION_LESS 3.4)
+  if (UNIX AND NOT CMAKE_C_COMPILER_VERSION VERSION_LESS 3.4)
     _get_clang_features(c11 CMAKE_C11_COMPILE_FEATURES)
     if (_result EQUAL 0)
       _get_clang_features(c99 CMAKE_C99_COMPILE_FEATURES)