If c_marshaller is provided during g_signal_new() registration, the
automatic va_marshaller will not be set. If we leave the c_marshaller as
NULL in the simple cases, both a c_marshaller and va_marshaller will be
set for us.
This is particularly helpful when dealing with stack traces from Linux
perf, which often cannot unwind the stack beyond the ffi_call_unix64
stack-frame on x86_64.
Related to GNOME/Initiatives#10
To help cross compilation, don't use glib-genmarshal in our
build. This is easy now that we have g_cclosure_marshal_generic().
In gobject/, add gmarshal.[ch] to git (making the existing entry
points stubs).
In gio/, simply switch to using g_cclosure_marshal_generic().
https://bugzilla.gnome.org/show_bug.cgi?id=652168