Re: bfd BLD-POTFILES.in dependencies

Removing $BLD_POTFILES from BFD-POTFILES.in was correct, but left a
hole in dependencies.
make[4]: Entering directory '/home/alan/build/gas/all/bfd/po'
make[4]: *** No rule to make target '../elf32-aarch64.c', needed by '/home/alan/src/binutils-gdb/bfd/po/bfd.pot'.  Stop.

	* Makefile.am (BUILT_SOURCES): Add BUILD_CFILES.
	* Makefile.in: Regenerate.