initial import of GCC 10.3.0. main changes include:

caveats:
- ABI issue between c++14 and c++17 fixed
- profile mode is removed from libstdc++
- -fno-common is now the default

new features:
- new flags -fallocation-dce, -fprofile-partial-training,
-fprofile-reproducible, -fprofile-prefix-path, and -fanalyzer
- many new compile and link time optimisations
- enhanced drive optimisations
- openacc 2.6 support
- openmp 5.0 features
- new warnings: -Wstring-compare and -Wzero-length-bounds
- extended warnings: -Warray-bounds, -Wformat-overflow,
-Wrestrict, -Wreturn-local-addr, -Wstringop-overflow,
-Warith-conversion, -Wmismatched-tags, and -Wredundant-tags
- some likely C2X features implemented
- more C++20 implemented
- many new arm & intel CPUs known

hundreds of reported bugs are fixed. full list of changes
can be found at:

https://gcc.gnu.org/gcc-10/changes.html

initial import of GCC 9.3.0. changes include:

- live patching support
- shell completion help
- generally better diagnostic output (less verbose/more useful)
- diagnostics and optimisation choices can be emitted in json
- asan memory usage reduction
- many general, and specific to switch, inter-procedure,
profile and link-time optimisations. from the release notes:
"Overall compile time of Firefox 66 and LibreOffice 6.2.3 on
an 8-core machine was reduced by about 5% compared to GCC 8.3"
- OpenMP 5.0 support
- better spell-guesser
- partial experimental support for c2x and c++2a
- c++17 is no longer experimental
- arm AAPCS GCC 6-8 structure passing bug fixed, may cause
incompatibility (restored compat with GCC 5 and earlier.)
- openrisc support