Changes

Turn on dependency checking on Inria CI

Only the "old school build" test uses --disable-dependency-generation.
This is also tested on both Travis and AppVeyor, so we have good release
coverage checking of this option.
 (commit: 11d0d66)

Silence CI warning for undefined variable
 (commit: e3dffa8)

Tighten dependencies for C files

The $(wildcard *.h) should only be there with
--disable-dependency-generation, since otherwise gcc -MM will be
determining exactly which header files should be checked.
 (commit: b3af8ca)

Restore compatibility with GNU make 3.81

It's the macOS default installed version still. The dependency generation
inadvertently relies on behaviour introduced in GNU make 3.82 a decade ago.

The fix in otherlibs/systhreads/Makefile also corrects missing
NATIVE_CPPFLAGS when generating st_stubs.n.d, so st_stubs.n.o now
correctly depends on caml/stacks.h instead of caml/stack.h
 (commit: 617522e)

Don't use -MG

It's a subtly broken thing to do, as discovered on the ARM workers on
Inria's CI.
 (commit: c948b8d)

Remove unneeded $(otherfiles) in runtime/Makefile

No longer required, and in fact causing breakages now that -MG isn't used.
 (commit: 942105f)

Update Changes
 (commit: 312ec98)