Add missing stdbool include for C compat.

Bug: https://github.com/android/ndk/issues/1920
Test: clang --sysroot out/soong/ndk/sysroot
          out/soong/ndk/sysroot/usr/include/**/*.h

Change-Id: Ic93ef129ae3c2014435699dcdca56215bdb00d59
diff --git a/include/android/performance_hint.h b/include/android/performance_hint.h
index 3c82d88..62d0423 100644
--- a/include/android/performance_hint.h
+++ b/include/android/performance_hint.h
@@ -53,6 +53,7 @@
  */
 
 #include <android/api-level.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <unistd.h>