unstable_external_project improvementsDefault arguments are added to add_project() in case some tags are not found in configure_options: '--prefix=@PREFIX@', '--libdir=@PREFIX@/@LIBDIR@', and '--includedir=@PREFIX@/@INCLUDEDIR@'. It was previously considered a fatal error to not specify them.
When the verbose keyword argument is not specified, or is false, command outputs are written on file in <builddir>/meson-logs/.
The LD environment variable is not passed any more when running the configure script. It caused issues because Meson sets LD to the CC linker wrapper but autotools expects it to be a real linker (e.g. /usr/bin/ld).