Reduce forks in AC_DEFINE.

Reduce forks in AC_DEFINE.

* lib/autoconf/general.m4 (_AC_DEFINE_Q_PRINT): New macro.
(_AC_DEFINE_Q): Use it to avoid forks for all AC_DEFINE and most
AC_DEFINE_UNQUOTED.
* lib/autoconf/fortran.m4 (_AC_FC_WRAPPERS): Properly quote #.
* tests/torture.at (Substitute and define special characters):
(Define to a 2000-byte string): Enhance tests to cover
AC_DEFINE_UNQUOTED.
(@%:@define header templates): Enhance test to cover #.

Signed-off-by: Eric Blake <ebb9@byu.net>