bootstrap broke in 4.2

[Mike Stump]

../../gcc/gcc/var-tracking.c: In function ‘variable_tracking_main’:
../../gcc/gcc/var-tracking.c:2961: warning: assuming signed overflow does not occur when assuming that (X - c) >= X is always true
../../gcc/gcc/var-tracking.c:2961: warning: assuming signed overflow does not occur when assuming that (X - c) >= X is always true
make[3]: *** [var-tracking.o] Error 1

:-(  Luckly, we had a chance to break it right before release...  :-)

Anyway else seeing these?