SDK settings.mk: Don't guess PLATFORM/PROCTYPE, and fix Mac OS X 64 bit

...rather, pass them from the build to the SDK installation via dk.mk.  (The SDK
installation is already platform-specific anyway, see the binary executables in
its bin/ directory, so there is no point in not fixing this at build time.  In
the future, the shipped settings.mk could of course be stripped to just the
parts relevant for a given platform, of course.)

Along the way, fixes some apparent "ppc" vs. "powerpc" typos in settings.mk.

Cherry picked from commit dea0398ee24eb278cdb14999efbf34d634454eaa "SDK
settings.mk: Don't guess PLATFORM/PROCTYPE" plus
e5ad31e2f784856506c28092166dc8704c84e868 "Fix Mac OS X 64 bit SDK settings.mk"
and b3db695a338f1acddbe46102138a0167fc346f58 "SDK: Split PLATFORMID at build
time rather than runtime" fix.

Conflicts:
	odk/settings/settings.mk

Change-Id: Ib8e0c03ad6dfd610aae58a61e32bdc61c785584f
Reviewed-on: https://gerrit.libreoffice.org/7748
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>