libhwc2.1: enable thread safety analysis for libdrmresource

Add -Wthread-safety compilation flag and fix the build break.

Bug: 285487960
Test: Build pass
Change-Id: I78ec84779aedfa2b8943c8266d43e7a41d54cbb6
Signed-off-by: Leo Chen <yinchiuan@google.com>
2 files changed