initial merge of GCC 10.3.0.

these three files are not yet finished merging:

gcc/config/rs6000/rs6000.c
libsanitizer/lsan/lsan_allocator.h
libsanitizer/sanitizer_common/sanitizer_platform_limits_po

initial merge of GCC 10.3.0.

these three files are not yet finished merging:

gcc/config/rs6000/rs6000.c
libsanitizer/lsan/lsan_allocator.h
libsanitizer/sanitizer_common/sanitizer_platform_limits_posix.h

our current GCC 9 sanitizers are newer than GCC 10's still, so that
may take a little to untease, so it's probable that more than
these 2 will need more changes.

rs6000.c has some changes related to ABI and supported functionality
that need to be merged forward.

show more ...

merge GCC 9.3.0.

merge GCC 8.4.0.

merge GCC 8.3.0 pass 1. will not compile yet. thare are still
about 25 files with merge issues.

revert local changes to riscv that come from the early gcc 4.8 era
patch for riscv that is now obsolete.

leave netbsd.h in place in case it is useful for the next re-porter.

Update to latest gcc changes. Default NetBSD to the medany cmodel.

Update gcc to use new ABI for RISCV

Add RISC-V support.