[CMake] Make simple source used for CMake checks a C file

The source being compiled is plain C, but using .cc extension forces it
to be compiled as C++ which requires a working C++ compiler including
C++ library which may not be the case when we're building compiler-rt
together with libcxx as part of runtimes build.

Differential Revision: https://reviews.llvm.org/D46152

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@331003 91177308-0d34-0410-b5e6-96231b3b80d8

Author: petrhosek

cmake/config-ix.cmake

@@ -125,7 +125,7 @@ set(COMPILER_RT_SUPPORTED_ARCH)
 # platform. We use the results of these tests to build only the various target
 # runtime libraries supported by our current compilers cross-compiling
 # abilities.
-set(SIMPLE_SOURCE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/simple.cc)
+set(SIMPLE_SOURCE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/simple.c)
 file(WRITE ${SIMPLE_SOURCE} "#include <stdlib.h>\n#include <stdio.h>\nint main() { printf(\"hello, world\"); }\n")
 
 # Detect whether the current target platform is 32-bit or 64-bit, and setup