[Upstream][runtimes] Don't depend on libpthread on Android

r362048 added support for ELF dependent libraries, but broke Android
build since Android does not have libpthread. Remove the dependency on
the Android build.

Differential Revision: https://reviews.llvm.org/D65098

Change-Id: I8d924f55b4d938144fce6b35a032640986525c2d
llvm-svn: 366734