mknative-gmp for GMP 6.2.1 and most platforms.

mknative-gmp output for GMP 6.2.0.

updates for GMP 6.1.2 and most platforms. run tested on i386, amd64,
sparc sparc64, earm, ofppc and mips64eb. build tested on most.

remove the earm* variants as they're now the same as the arm* on

updates for GMP 6.1.2 and most platforms. run tested on i386, amd64,
sparc sparc64, earm, ofppc and mips64eb. build tested on most.

remove the earm* variants as they're now the same as the arm* ones.

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fix definition of __GMP_CC.

updates for GMP 5.1.3, and new build files for most platforms.

remove references to my src/obj trees, and make a note about avoiding
this in the future / should automate it too.

(re-)generate mknative-gcc files for many platforms.
(re-)generate the gmp files for many platforms.