byacc: update to 20210328.

2021-03-28  Thomas E. Dickey  <dickey@invisible-island.net>

* reader.c: ignore bison's "%empty" extension

* reader.c, defs.h:  %debug was a trivial bison "extension", mark
it as such

* yacc.1: use italics in a few places where bold was inappropriate

* test/btyacc/varsyntax_calc1.tab.c,
test/btyacc/varsyntax_calc1.tab.h, test/btyacc/expr.oxout.tab.c,
test/btyacc/expr.oxout.tab.h, test/btyacc/inherit1.tab.c,
test/btyacc/inherit1.tab.h, test/btyacc/inherit2.tab.c,
test/btyacc/inherit2.tab.h, test/btyacc/ok_syntax1.tab.c,
test/btyacc/ok_syntax1.tab.h, test/btyacc/err_inherit3.tab.c,
test/btyacc/err_inherit3.tab.h, test/btyacc/err_inherit4.tab.c,
test/btyacc/err_inherit4.tab.h, test/btyacc/btyacc_calc1.tab.c,
test/btyacc/btyacc_calc1.tab.h, test/btyacc/btyacc_demo.tab.c,
test/btyacc/btyacc_demo.tab.h, test/btyacc/btyacc_destroy1.tab.c,
test/btyacc/btyacc_destroy1.tab.h,
test/btyacc/btyacc_destroy2.tab.c,
test/btyacc/btyacc_destroy2.tab.h,
test/btyacc/btyacc_destroy3.tab.c,
test/btyacc/btyacc_destroy3.tab.h, test/btyacc/calc1.tab.c,
test/btyacc/calc1.tab.h, test/yacc/varsyntax_calc1.tab.c,
test/yacc/varsyntax_calc1.tab.h, test/yacc/expr.oxout.tab.c,
test/yacc/expr.oxout.tab.h, test/yacc/ok_syntax1.tab.c,
test/yacc/ok_syntax1.tab.h, test/yacc/calc1.tab.c,
test/yacc/calc1.tab.h:  regen

* reader.c:  add union tag to YYSTYPE structure for compatibility
with a feature which bison copied from Solaris yacc (request by
Ella Stanforth)

* configure: regen

* config_h.in: update for _Noreturn feature

* aclocal.m4: updated to work with autoheader

* defs.h: apply syntax change needed for _Noreturn keyword

* package/byacc.spec, package/debian/rules: use stdnoreturn

* VERSION, package/byacc.spec, package/debian/changelog,
package/mingw-byacc.spec, package/pkgsrc/Makefile:  bump

2021-03-20  Thomas E. Dickey  <dickey@invisible-island.net>

* configure: regen

* aclocal.m4:  resync with my-autoconf (adds --enable-stdnoreturn
option)

(fcambus)