aarch64: Add -mtune=neoverse-512tvb (#1845932)

backport PCH tweaks (#2030878)

avoid cycling on certain subreg reloads (PR rtl-optimization/96796, #2028798)

when linking against libgcc_s, link libgcc.a too (#2022588)

add -Wbidi-chars patch (#2008392)

fix mangling of lambdas in default args (PR c++/91241, #1981822)
add a few Provides: bundled

revert upstream PR85873 gcc-8 fix, apply the fix from gcc-9 (#1960701)
fix 'this' adjustment for devirtualized call (PR c++/100797, #1965951)

update from GCC 8.5 release (#1946758)
this includes a fix for PR target/87839 (#1958295)

remove support for demangling GCC 2.x era mangling schemes (#1668394)

update from GCC 8.4 release (#1946758)

back out the PR97236 patch

fix bad use of VMAT_CONTIGUOUS (PR tree-optimization/97236, #1925632)

update from GCC 8.4 release (#1868446)
remove symlinks to 32-bit versions of these static libraries: libasan.a,

backport aarch64 LSE atomics (#1821994)

consider negative edges in cycle detection (#1817991, PR gcov-profile/91601)
fix Fortran debug info for arrays with descriptors (#1655624,
fix wrong code emitted for movv1qi on s390x (#1784758, PR target/92950)

update from Fedora gcc-8.3.1-5 (#1747157)
use unspec_volatile for darn (PR target/91481, #1760205, CVE-2019-15847)