The signed characters in scripts are causing warnings with GCC 4 on
systems with proper string functions (with char*, not signed char* as
parameters). Some could be kept signed but most had to be reverted to
normal chars.

Detailed changlog:

fixdep.c:
	- is_defined_config() just used memcmp so it was changed to use
	  signed strings.
	- define_config() was called with both signed and "normal"
	  strings. Since no string functions were used the parameter was
	  changed to void *.
	- use_config() only called is_defined_config() and
	  define_config() so it could use signed strings.
	- parse_dep_file() used strchr() so it needed to lose the
	  signed.
docproc.c:
	- All signed strings were removed because they were all
	  directly or indirectly used in string functions.
split-include.c:
	- The only signed string here was removed because of usage with
	  strstr().

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>