Log message:
lang/gccX: switch from USE_LANGUAGES=c99 to USE_CC_FEATURES/FORCE_C_STD.

Log message:
gcc*: replace gnarly cargo-culted extract logic with EXTRACT_ONLY

Log message:
gcc10*: update to 10.5.0

The list of PR's fixed since 10.4.0 can be found here:

https://gcc.gnu.org/bugzilla/buglist.cgi?bug_status=RESOLVED&resolution=FIXED&target_milestone=10.5

which includes 3 C, 25 C++, 4 debug, 17 libstdc++, and many others for the
internals.

Log message:
lang/gcc*: USE_TOOLS+=sed, not sed:run.

As far as I can tell, gcc needs this at build-time, not at run-time.

https://mail-index.netbsd.org/tech-pkg/2023/06/02/msg027624.html

Log message:
lang/gcc*: Set CC_FOR_BUILD and CXX_FOR_BUILD if cross-compiling.

Verified gcc6 and gcc7 cross-compile on NetBSD, at least if the
gcc-fortran option is disabled.  gcc8 and gcc9 have trouble because
of python (why do these have a full dependency on python?); gcc10 and
gcc12 are missing gcc/config/mips/netbsd64.h; gcc12 and gcc13 have a
cross-compile bug with missing __LIBGCC_*__ macros -- but in any
case, setting CC_FOR_BUILD and CXX_FOR_BUILD is obviously necessary
for cross-compilation.  Conditional on USE_CROSS_COMPILE, so no harm
to native builds.

Log message:
gcc10: set LANGS before including Makefile.common

that includes options.mk which may modify LANGS

Log message:
gcc10: add note that gcc10-libjit shares Makefile.common

Log message:
gcc10: set PATCHDIR, DISTINFO_FILE

Log message:
gcc10: split off some parts of the Makefile into Makefile.common

Log message:
gcc10: make options.mk standalone