Use 'cc' as default compiler.

Index: make_ffi.py
--- make_ffi.py.orig
+++ make_ffi.py
@@ -76,7 +76,7 @@ def doit(vex_path):
     errs = []
     for cpp in cpplist:
         cmd = [cpp, '-I' + vex_path, os.path.join("pyvex_c", "pyvex.h")]
-        if cpp in ('cl', 'clang', 'gcc', 'cc', 'clang++', 'g++'):
+        if cpp in ('cc'):
             cmd.append("-E")
         try:
             p = subprocess.Popen(cmd,