win32: Disable marshal rebuilds for GLib

Add --disable-rebuilds to the GLib configure args, to avoid
re-generating the gobject/gmarshal.[ch] files with an incorrect
glib-genmarshal from the build system. The system glib-genmarshal
is a later version for me, and generates an unbuildable gmarshal.c
that references g_value_get_schar.
win32: Update fontconfig cross-compilation patch

Make sure fontconfig doesn't use the Win32 link
flags as well as CFLAGS, as it breaks compilation
of the build-time tools.
win32: Make the installer build find translations correctly.

At some point my intltool.m4 started defining DATADIRNAME as 'share'
instead of 'lib', and putting the repsnapper translation files in
there, breaking the NSIS script. Substitute the correct value at
configure time so it works either way.