toolchain_build: Force GCC build to recognize "system" limits.h

toolchain_build: Force GCC build to recognize "system" limits.h

The GCC build always creates a limits.h header in one of GCC's special
include directories.  The way it's supposed to work is that this file
gets the "system" limits.h (i.e. for us, the one from newlib) via some
complex #include_next chicanery.  The GCC build decides whether to do
that based on whether it sees a limits.h in the "system" include
directory (i.e. for us, the sysroot's include/).  Since we build GCC
in a hermetic environment, there are no newlib headers for it to see
during this part of the build and it makes the wrong decision.
Fortunately, it's straightforward to override its decision with a
variable on the make command line.

BUG= http://code.google.com/p/nativeclient/issues/detail?id=3190
TEST= trybots

R=sbc@chromium.org,bradnelson@google.com

Committed: https://src.chromium.org/viewvc/native_client?view=rev&revision=10387

[bradn, 2012-12-05 19:58:29]

lgtm