Do not explicitly link ucrt, ucrtbase

This was required before MinGW's default crt was set to ucrt.  In the
new setting, libmsvcrt.a is similar to libucrt.a and is implicitly
linked-in by the Clang driver.  Not explicitly linking in ucrt avoids
the link-order issue discussed in
https://github.com/android/ndk/issues/1198.

Test: m native-host-cross, go/android-llvm-windows-testing.
Change-Id: Idc125e550cae2f0eb812ca310d1d4be898a29ab4