Update to the 20150118 snapshot of GCC 5.0.

libgcj-5.0.pc is now properly called libgcj-5.pc; adjust pkg-plist.

libffi is broken on FreeBSD i386 since 2015-01-11, cf.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64779, so disable it
for the time being.