[sanitizer] Define SANITIZER_USE_GETAUXVAL for Android

Summary:
Android for API level >= 21 has `getauxval`. Enable `SANITIZER_USE_GETAUXVAL`
when those requirements are met. Correct a typo in the header.

Reviewers: alekseyshl

Reviewed By: alekseyshl

Subscribers: srhines, llvm-commits, kubamracek

Differential Revision: https://reviews.llvm.org/D40260

llvm-svn: 318775