check for GCC

git-svn-id: svn+ssh://svn.cprover.org/srv/svn/cbmc/trunk@6494 6afb6bc1-c8e4-404c-8f48-9ae832c5b171

Author: kroening

regression/ansi-c/MMX1/main.c

@@ -4,11 +4,14 @@
 
 int main()
 {
+  // This is a gcc extension
+  #ifdef __GNUC__  
   __m64 x;
 
   long long unsigned di;
 
   x=(__m64)di;  
+  #endif
 
   return 0;
 }