Disable -Wthread-safety-negative

ART used to turn on -Wthread-safety-negative, but at some point the
build started adding -Wno-thread-safety-negative later on the command
line.  That is being fixed, but causes new warnings in ART.  Disable
-Wthread-safety-negative for now.

Bug: 144045034
Test: mma
Change-Id: I3a2edd4472b6ff7beff08289c45997694f543668
1 file changed