devel/gettext-tools: Fix build with non-default prefix
Building this port with a non-default prefix gives the following:
msgmerge.c:35:10: fatal error: 'textstyle.h' file not found #include <textstyle.h> ^~~~~~~~~~~~~ 1 error generated. *** [msgmerge-msgmerge.o] Error code 1
That is, textstyle.h is present in the appropriate location under
our prefix, alas it's not found.
USES=localbase addresses this.
PR: 258286
Approved by: tijl (maintainer)