scanner: sort out scanner logging functions

First, make the rules and xkb scanners/parsers use the same logging
functions instead of rolling their own.

Second, use the gcc ##__VA_ARGS extension instead of dealing with C99
stupidity. I hope all relevant compilers support it.

Signed-off-by: Ran Benita <ran234@gmail.com>
build: fix configure test for yacc

It only works if 'bison' or 'byacc' are provided, but sometimes byacc
is installed as plain 'yacc'. The check fails for that.

I broke this in bdd8c11, restore Daniel's retrospectively clever check.

Signed-off-by: Ran Benita <ran234@gmail.com>
Move src/xkbcomp/scanner-utils.h to src/

As we'll use it for things unrelated to xkbcomp.

Signed-off-by: Ran Benita <ran234@gmail.com>