gcc pr 95921. the m68k sqrt rtl handles excess precision wrong. I
couldn't figure out how to make gcc generate the insn only for long
double, but since long double usage is rare anyway, just remove it.
this can be replaced with a proper fix later if there's ever one
upstream.
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.