* Makefile.in (MACHMODE_H): Add @extra_modes_file@.
* configure.in: If $srcdir/config/${cpu_type}/${cpu_type}-modes.def
exists, substitute its pathname as @extra_modes_file@, define
EXTRA_MODES_FILE to be an appropriate string to #include it
with, and define EXTRA_CC_MODES to 1.
* machmode.def: Update comments. Include EXTRA_MODES_FILE if
it's defined. Get rid of redundancy in calling sequence for
CC; don't use it to define CCmode, to avoid a warning.
* libgcc2.c: Include symcat.h for the sake of machmode.def.