mknative-gcc for GCC 10 and almost all platforms. one of the
myriad of arm platforms, and the powerpc* platforms are not
yet done.

mknative-gcc for GCC 8.3 and all ports.

regen mknative for everyone after:

- NETBSD_ENABLE_PTHREADS removed (default always)
- HAVE_GNU_INDIRECT_FUNCTION enabled for some platforms
- switch to dragondfly bsd locale routines after christos

regen mknative for everyone after:

- NETBSD_ENABLE_PTHREADS removed (default always)
- HAVE_GNU_INDIRECT_FUNCTION enabled for some platforms
- switch to dragondfly bsd locale routines after christos made them work for us

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enable the workarounds for cortex a53 errata 835769 and 843419 by default.

First pass at mknative for aarch64, based on mrg's work.