* data/c.m4 (b4_int_type): Use yysigned_char instead of signed char,

* data/c.m4 (b4_int_type): Use yysigned_char instead of signed char,
for portability to K&R hosts.  Fix typo: signed char is guaranteed
only to 127, not to 128.
* data/glr.c (yysigned_char): New type.
* data/yacc.c (yysigned_char): Likewise.
* tests/regression.at (Web2c Actions): signed char -> yysigned_char.