Bug 1042878 - part 0 - remove 'SHELL := ksh' assignment in layout/build/Makefile.in; r=glandium

This could be a separate bug, but it's easiest to fix it here, since
removing this assignment enables removing the Makefile.in later.

Untested, but if everything else builds without a custom SHELL
assignment, this module should too.
Bug 1042878 - part 1 - make most *CFLAGS variables from configure lists in moz.build; r=glandium
Bug 1042878 - part 2 - move MOZ_CAIRO_CFLAGS et al additions to C*FLAGS into moz.build; r=glandium