> Here is the diff of the latest commit. (Patch attached anyway).

Thanks.  I tried with the patch.patch you attached.  When trying a gtk
build I get:

../../src/xfaces.c:5434: Emacs fatal error: assertion failed: lface_fully_specified_p (XVECTOR (lface)->contents)
Fatal error 6: Aborted
Backtrace:
../src/bootstrap-emacs[0x67e32f]
../src/bootstrap-emacs[0x6344c8]
../src/bootstrap-emacs[0x74fb6f]
../src/bootstrap-emacs[0x5a8e43]
../src/bootstrap-emacs[0x5a83f8]
../src/bootstrap-emacs[0x59bccf]
../src/bootstrap-emacs[0x436ad1]
../src/bootstrap-emacs[0x4fd0ad]
../src/bootstrap-emacs[0x76376c]
../src/bootstrap-emacs[0x63530c]
../src/bootstrap-emacs[0x635860]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f68217952e1]
../src/bootstrap-emacs[0x4151aa]
/bin/bash: Zeile 2: 12088 Abgebrochen            EMACSLOADPATH= '../src/bootstrap-emacs' -batch --no-site-file --no-site-lisp --eval '(setq load-prefer-newer t)' -l bytecomp -f byte-compile-refresh-preloaded -f batch-byte-compile ../../lisp/cus-face.el
Makefile:280: die Regel für Ziel „../../lisp/cus-face.elc“ scheiterte
make[2]: *** [../../lisp/cus-face.elc] Fehler 134
Makefile:784: die Regel für Ziel „../../lisp/cus-face.elc“ scheiterte
make[1]: *** [../../lisp/cus-face.elc] Fehler 2
make[1]: *** Es wird auf noch nicht beendete Prozesse gewartet...

../../src/xfaces.c:5434: Emacs fatal error: assertion failed: lface_fully_specified_p (XVECTOR (lface)->contents)
Backtrace:
../src/bootstrap-emacs[0x67e32f]
../src/bootstrap-emacs[0x6344c8]
../src/bootstrap-emacs[0x74fb6f]
../src/bootstrap-emacs[0x5a8e43]
../src/bootstrap-emacs[0x5a83f8]
../src/bootstrap-emacs[0x59bccf]
../src/bootstrap-emacs[0x436ad1]
../src/bootstrap-emacs[0x4fd0ad]
../src/bootstrap-emacs[0x76376c]
../src/bootstrap-emacs[0x63530c]
../src/bootstrap-emacs[0x635860]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f0e8f3a32e1]
../src/bootstrap-emacs[0x4151aa]
/bin/bash: Zeile 2: 12090 Abgebrochen            EMACSLOADPATH= '../src/bootstrap-emacs' -batch --no-site-file --no-site-lisp --eval '(setq load-prefer-newer t)' -l bytecomp -f byte-compile-refresh-preloaded -f batch-byte-compile ../../lisp/faces.el
Makefile:280: die Regel für Ziel „../../lisp/faces.elc“ scheiterte
make[2]: *** [../../lisp/faces.elc] Fehler 134
Makefile:784: die Regel für Ziel „../../lisp/faces.elc“ scheiterte
make[1]: *** [../../lisp/faces.elc] Fehler 2
make[1]: Verzeichnis „/home/martin/emacs-git/trunk/obj-gtk/src“ wird verlassen
Makefile:424: die Regel für Ziel „src“ scheiterte
make: *** [src] Fehler 2

and a similar crash on Windows.  Before proceeding to dig into this
I'd like to hear your ideas.

> https://github.com/Ergus/Emacs/commit/4943087027acd3f2c7a54a092b64bc839ef8850e

Is there any way to get the diffs wrt current master on that site?  I
never use github for such a thing and my browser settings are quite
restrictive.