msi: Use -fno-builtin to avoid warnings with gcc 4.1.1.

[Mike McCormack]

I investigated this and have reported a bug:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28437

In summary, gcc 4.1.2 seems to ignore all but the last -fno-builtin-* 
flag out of many...

$ cat b.c
int iswalpha(unsigned short);
$ gcc -fno-builtin-iswalpha -c b.c
$ gcc -fno-builtin-iswalpha -fno-builtin-iswalnum -c b.c
b.c:1: warning: conflicting types for built-in function ‘iswalpha’

Mike