Fix attribution of Linux/ARM/Bionic: it's 4.21
Fix attribution of Linux/ARM/Bionic: it's 4.21

A mismerge inadvertently attributes the 4.20 build as being the one for
Android's "bionic" libc, whereas the bionic build really is 0.4.21.
Compare http://git.io/vmHcD#L33-L34 (lines 33-34 of commmit
rebolsource/r3@235d923) to confirm the proper id.

The difference between Linux/ARM glibc and bionic builds is that
bionic's loader _requires_ position-independent executables (PIEs).
Most glibc-based Linux/ARM works fine with PIEs as well, so the 0.4.20
vs 0.4.21 doesn't matter much on non-bionic systems in practice. We
could arguably also unify those two build targets again, under 0.4.20 +
PIE. But as PIE slightly increases binary size (~5% for R3, in a quick
test at the time of this writing) and that size difference may matter
more on ARM-based systems, we'll leave the two targets for the time
being.

giuliolunati/ren-c,rgchris/ren-c,mbk/ren-c,draegtun/ren-c,codebybrett/ren-c,mbk/ren-c,kealist/ren-c,giuliolunati/ren-c,mbk/ren-c,hostilefork/rebol,rgchris/ren-c,kealist/ren-c,rgchris/ren-c,mbk/ren-c,hostilefork/rebol,giuliolunati/ren-c,draegtun/ren-c,codebybrett/ren-c,hostilefork/rebol,hostilefork/rebol,draegtun/ren-c,draegtun/ren-c,kealist/ren-c,giuliolunati/ren-c,codebybrett/ren-c,kealist/ren-c,codebybrett/ren-c,codebybrett/ren-c,draegtun/ren-c,giuliolunati/ren-c,rgchris/ren-c,kealist/ren-c,codebybrett/ren-c,hostilefork/rebol,kealist/ren-c,rgchris/ren-c,hostilefork/rebol,draegtun/ren-c