8173107: Fix autoconf/spec.gmk mismatches
Reviewed-by: erikj, dholmes

8167424: Various trivial fixes in build system
Reviewed-by: erikj, tbell

8031767: Support system or alternative implementations of zlib
Reviewed-by: alanb, erikj

8138761: Improved handling of libffi, and cleanup of libraries.m4
Reviewed-by: erikj