[compiler-rt][Android] Use correct builtins library name for tests

The builtins library name is special on Android:

 * There is an "-android" suffix.

 * For the compiler-rt i386 architecture, Android targets i686 (in the
   triple and in the builtins library filename)

With this change, check-builtins works with Android.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D82149