[PATCH] make include path handling gcc compatible

[PATCH] make include path handling gcc compatible

Search include paths in same order as gcc does.

In other words search directories specified with -I before system
directories.

This fixes a bug reported by a few persons after the kernel switched
over to use -isystem to specify where to find compiler specific include files.

Sparse now supports the following include path relevant options:
-I dir		Add dir to list of directories to search for. Search dir
		before system dirs. Used for both <> and "" includes.
-I-		Split include path - previous -I dir paths only used for
		include "".
		Also disable searching same dir as input file.
-isystem dir	Add dir first in row of system dirs to search.
-dirafter dir	Add dir in end of system dirs to search.
-nostdinc	Discard all defined system dirs

The -iwithprefix, -iprefix and -iwithprefixbefore options are not not
supported and silently ignored. gcc discourage use of these options.