intl: always picify

libintl is included in several shared libraries (at least
libinproctrace.so and libctf.so): unconditionally picify with code
borrowed from libiberty configure.  (It's not performance-critical, so
don't bother making separate PIC and non-PIC libraries like libiberty
does.)

intl/ChangeLog
2021-02-02  Nick Alcock  <nick.alcock@oracle.com>

	* aclocal.m4: include picflag.m4.
	* configure.ac (PICFLAG): Add and substitute.
	* Makefile.in (PICFLAG): New.
	(COMPILE): Use it.
	* configure: Regenerate.