Use <condition_variable> and <mutex.h> from MinGW

New MinGW prebuilts update includes pthreads and C++11 threads support.
Use mutex.h and condition_variable provided by MinGW.

Test: Build AOSP with new MinGW prebuilts
Change-Id: Ia8f890f86652612df3fc2618c2bfbb450a5a2f52
6 files changed