Warnings

Created by: o11c

• Update warning list for GCC 5.
• Change DIAG_W to be fatal too. But both this and DIAG_X should be carefully looked at to see whether they currently, or in the future, could be changed to DIAG_E or must be DIAG_I.
• Make sure old-but-supported GCC versions are still tested in dev mode.
• Add asan and lto builds
• Fix tests not failing the build.
• Dump configure output.