* Parse CFLAGS that can be passed using a whitelist
I went through GCC's man page and selected flags that can safely be
passed to GCC and that can be useful to syntax checking. These include:
- -I/-i* include flags
- preprocessor flags such as -D
- -W* warning flags
- -O* optimization flags
- most -f options
- -m arch dependent options
* Fix CFLAGS tests: -Idir is now parsed to -I dir
* Added two tests for flags we want or don't want to pass.
* Also check for / in addition to s:sep
