Log Message:
editors/mg: Mask -Werror

mg adds the -Werror flag after CFLAGS, so any suppressed warning gets
reenabled.  Starting with gcc4.6, unused-but-set-variable warnings are
issued which breaks the build.  Passing Wno-unused-but-set-variable by
the package makefile (as a function of compiler version) doesn't work.
The easiest solution is just to disable -Werror.  In this case through
the makefile rather than updating a patch.