one-true-awk: import 20210221 (1e4bc42c53a1) which fixes a number of bugs

Import the latest bsd-features branch of the one-true-awk upstream:

o Move to bison for $YACC
o Set close-on-exec flag for file and pipe redirects that aren't std*
o lots of little fixes to modernize ocde base
o free sval member before setting it
o fix a bug where a{0,3} could match aaaa
o pull in systime and strftime from NetBSD awk
o pull in fixes from {Net,Free,Open}BSD (normalized our code with them)
o add BSD extensions and, or, xor, compl, lsheift, rshift (mostly a nop)

Also revert a few of the trivial FreeBSD changes that were done slightly
differently in the upstreaming process. Also, our PR database may have
been mined by upstream for these fixes, and Mikolaj Golub may deserve
credit for some of the fixes in this update.

Suggested by: Mikolaj Golub <to.my.trociny@gmail.com>
PR: 143363,143365,143368,143369,143373,143375,214782
Sponsored by: Netflix

Merge from upstream at 4189ef5d from https://github.com/onetrueawk/awk.git

Note: this backs out a number of changes we've made to awk because
they aren't upstream, but are on the vendor branch. Those will be
reapplied. svn makes it needlessly difficult to know which ones, but
at least r315426, r301289, and maybe r301691, though there may be
others too. None of these are critical, so bisecting through this
point is safe for all but awk regression tests :).