Disable 64bit file position on old 32 bit Androids.

This is needed for building LLVM on Android with new NDK (newer
than r15c) and API level < 24. Android C library (Bionic) didn't have
support for 64 bit file position until Android N.

Differential Revision: https://reviews.llvm.org/D37314

llvm-svn: 312389