libbacktrace: test --compress-debug-sections=ARG for each ARG

This should fix a testsuite problem with Solaris ld that supports zlib
but not zlib-gabi.

	* configure.ac: Test --compress-debug-sections=zlib-gnu and
	--compress-debug-sections=zlib-gabi separately, setting new
	automake conditionals.
	* Makefile.am (ctestg, ctestg_alloc): Only build if
	HAVE_COMPRESSED_DEBUG_ZLIB_GNU.
	(ctesta, ctesta_alloc): Only build if
	HAVE_COMPRESSED_DEBUG_ZLIB_GABI.
	(ctestzstd_alloc): New test if HAVE_COMPRESSED_DEBUG_ZSTD.
	* configure, Makefile.in: Regenerate.