libbinder: unused-result warning

Bug: 388886755
Test: check logs on boot
Change-Id: I70faf816a15574018b1df688950173af7af640bc
diff --git a/libs/binder/Android.bp b/libs/binder/Android.bp
index aac369d..fb00d4f 100644
--- a/libs/binder/Android.bp
+++ b/libs/binder/Android.bp
@@ -269,6 +269,7 @@
         "-Wzero-as-null-pointer-constant",
         "-Wreorder-init-list",
         "-Wunused-const-variable",
+        "-Wunused-result",
         "-DANDROID_BASE_UNIQUE_FD_DISABLE_IMPLICIT_CONVERSION",
         "-DANDROID_UTILS_REF_BASE_DISABLE_IMPLICIT_CONSTRUCTION",
         // Hide symbols by default and set the BUILDING_LIBBINDER macro so that