libtextstyle: be sure to have ostream_printf and hyperlink support

Older versions of libtextstyle do not support them, rule them out.

Reported by Lars Wendler
https://lists.gnu.org/r/bug-bison/2020-07/msg00030.html

and by Arnold Robbins
https://lists.gnu.org/r/bug-bison/2020-07/msg00041.html and
https://lists.gnu.org/mailman/private/gawk-devel/2020-July/003988.html

and by Nelson H. F. Beebe
https://lists.gnu.org/mailman/private/gawk-devel/2020-July/003993.html

With support from Bruno Haible in gnulib
https://lists.gnu.org/r/bug-gnulib/2020-08/msg00000.html
thread starting at
https://lists.gnu.org/r/bug-gnulib/2020-07/msg00148.html

* configure.ac: Require libtextstyle 0.20.5.
* gnulib: Update.

m4/.gitignore

@@ -67,7 +67,6 @@
 /intlmacosx.m4
 /intmax.m4
 /intmax_t.m4
-/inttypes-pri.m4
 /inttypes.m4
 /inttypes_h.m4
 /isnan.m4
@@ -97,7 +96,6 @@
 /locale-ja.m4
 /locale-zh.m4
 /locale_h.m4
-/localtime-buffer.m4
 /lock.m4
 /longlong.m4
 /lstat.m4
@@ -117,6 +115,7 @@
 /msvc-inval.m4
 /msvc-nothrow.m4
 /multiarch.m4
+/musl.m4
 /nls.m4
 /nocrash.m4
 /non-recursive-gnulib-prefix-hack.m4