Include NDK CRT object variants in the sysroot.

The actual NDK distribution will overwrite these (they're branded with
the platform's version information, which isn't what the NDK wants to
brand apps with), but including them here makes it easier to iterate
on the platform sysroot in situations that don't require a strictly
correct NDK sysroot.

Bug: None
Test: None
Change-Id: I22d4de9caa8753578a2327b1ece0deb005708b08