Directories for gcc

[Axel Kittenberger]

> A default set of directories is compiled in: look at gcc/protoize.c in
> the source. You can see these from a binary gcc by compiling or
> preprocessing any source with the '-v' switch.
>
> You can also always add more directories on the command line using '-I'
> or '-isystem'. You can probably also edit them into the compiler specs
> file (<prefix>/lib/gcc-lib/<host>/version/specs) but I don't know much
> about specs files. If you need more directories for a configure/make
> source tree then you set -I switches in the CC or CFLAGS environments,
> e.g. (bash)

Might be worth a mention additionally if you don't want it to look in 
/usr/include for headers specify the command parameter:
--nostdinc

- Axel