Fix bugprone-macro-parentheses warnings

Bug: 150783705
Test: WITH_TIDY=1 make
Change-Id: If47b7adaa5f3ba3c518fb0be48f0ffdc81d204b2
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 331e92c..8bc897a 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -68,7 +68,7 @@
 #define PTHREAD_ONCE_INIT 0
 
 #if __ANDROID_API__ >= 24
-#define PTHREAD_BARRIER_SERIAL_THREAD -1
+#define PTHREAD_BARRIER_SERIAL_THREAD (-1)
 #endif
 
 #if defined(__LP64__)