trusty: add warn_unused_result for mmap() & munmap() am: 277c60c09b

Original change: https://android-review.googlesource.com/c/trusty/external/musl/+/3256820

Change-Id: I78416690f945bdf3035d78e5da705d5a428dc96b
Signed-off-by: Automerger Merge Worker <[email protected]>