libctf, dedup: add new configure option --enable-libctf-hash-debugging

libctf, dedup: add new configure option --enable-libctf-hash-debugging

Add a new debugging configure option, --enable-libctf-hash-debugging,
off by default, which lets you configure in expensive internal
consistency checks and enable the printing of debugging output when
LIBCTF_DEBUG=t before type deduplication has happened.

In this commit we just add the option and cause it to turn ctf_assert
into a real, hard assert for easier debugging.

libctf/
	* configure.ac: Add --enable-libctf-hash-debugging.
	* aclocal.m4: Pull in enable.m4, for GCC_ENABLE.
	* Makefile.in: Regenerated.
	* configure: Likewise.
	* config.h.in: Likewise.
	* ctf-impl.h [ENABLE_LIBCTF_HASH_DEBUGGING]
	(ctf_assert): Define to assert.