Log Message:
editline: adjust libedit.pc file due to BUILDLINK_FNAME_TRANSFORM

We have questionable BUILDLINK_FNAME_TRANSFORMs in the bl3.mk that
transform include/editline/readline.h into include/readline/readline.h.

So if libedit.pc file says to use -I${PREFIX}/include/editline that
works fine when building stuff outside of pkgsrc but not inside of pkgsrc.

Workaround is to put both -I${PREFIX}/include/editline and
-I${PREFIX}/include/readline in the pc file, in that order of preference.