Merge pull request #428 from andlaus/make_quadmath_test_more_strict

fix test for HAVE_QUAD on some instances of ubuntu 13.10

cmake/Modules/FindQuadmath.cmake

@@ -12,11 +12,12 @@ include(CMakePushCheckState)
 
 cmake_push_check_state()
 list(APPEND CMAKE_REQUIRED_LIBRARIES "quadmath")
-CHECK_C_SOURCE_COMPILES("
+CHECK_CXX_SOURCE_COMPILES("
 #include <quadmath.h>
 
 int main(void){
     __float128 foo = sqrtq(123.456);
+    foo = FLT128_MIN;
 }" HAVE_QUAD)
 cmake_pop_check_state()