utils: add pwrite64 to Compat.h for Mac

Compat.h has lseek64 and pread64, but it's missing pwrite64.

Change-Id: I02b4adf5a5e15e55e008ff1ba8113a75faf1c4e9
diff --git a/include/utils/Compat.h b/include/utils/Compat.h
index c5f9d6a..b2ba55e 100644
--- a/include/utils/Compat.h
+++ b/include/utils/Compat.h
@@ -33,6 +33,10 @@
     return pread(fd, buf, nbytes, offset);
 }
 
+static inline ssize_t pwrite64(int fd, const void* buf, size_t nbytes, off64_t offset) {
+    return pwrite(fd, buf, nbytes, offset);
+}
+
 #endif /* __APPLE__ */
 
 #if defined(_WIN32)