mknative-gcc for gcc 9.3.0 and arm64, alpha, hppa, ia64, m68*, mipseb,
powerpc, riscv*, sh3*, sparc*, vax.

move data from README.gcc8 to README.gcc9.

rebuild mknative GCC 6.4 for these targets:
arm armeb earmeb earmhf earmhfeb earmv4eb
earmv6 earmv6eb earmv6hf earmv6hfeb
earmv7 earmv7eb earmv7hf earmv7hfeb
hppa ia64 m68000 m68k
mips64eb mips6

rebuild mknative GCC 6.4 for these targets:
arm armeb earmeb earmhf earmhfeb earmv4eb
earmv6 earmv6eb earmv6hf earmv6hfeb
earmv7 earmv7eb earmv7hf earmv7hfeb
hppa ia64 m68000 m68k
mips64eb mips64el mipseb mipsel
powerpc64 sh3eb sh3el vax

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merge GCC 4.8 build.

alpha and hppa mknative-gcc files.