Compiling with -ansi instead of --std=c99 for compatibility with old compilers.

I didn't really want to do this because I forfeit two features:

1. Mixed declarations and code (I really miss this one)
2. Flexible array members (e.g. for string structure)

Also, compiling with -ansi made it more difficult to access certain built-in
functions properly, so I created two header files sys_math.h and sys_stdio.h
to compensate for that.  That way I get the proper declarations for round,
trunc, fabs, pow, and snprintf.