new patch: 0017-c++-abi-break.diff fixes a C++ ABI break regression.
0010-static-pie-support.diff was removed as it doesn't apply anymore,
and forward-porting it requires arcane knowledge of GCC details.
the patches 0018 and 0019 have been copied from GCC 7.3.0. the static
pie patch from GCC 6.4.0, renumbered 0020, depends on the reversions
they make.
GCC 6.4.0 has one big advantage over 6.3.0: it is shipped as .tar.xz,
shaving 30 MB from its download size, and also considerably speeding
up the extraction process.
All patches are copies of the GCC 6.3.0 ones, except
0004-posix_memalign.diff which was rebased to apply cleanly.
0014-ubsan-empty-string-fix.diff was removed, since it was upstreamed.
this feature is still experimental and requires manually setting a
LINUX_ARCH make variable matching the target. automatic mapping will
be added later. if LINUX_ARCH is not set, header installation is
skipped.
