Remove --allow-multiple-definitions for 32-bit Windows

Bug: http://b/109759970
Bug: http://b/91353691

There are no multiple-defintion errors after switching to clang-r339409
and libc++.

Test: m native-host-cross
Change-Id: I5576b3894ed1d88c9b2e5f4d92e1d3bfadfb029b