In LTO mode the backend constructs a target exclusively from command line flags,
without opportunity to accept code gen arguments from Clang. Clang does not
currently pass the -emulated-tls parameter for Android, even though it defaults
to emulated TLS for Android in non-LTO builds. Until this is fixed upstream, we
can explicitly specify that the LTO output for Android should use emulated TLS.
Test: build libandroid with LTO, verified that it uses __emutls_get_address
rather than __tls_get_addr.
Change-Id: I18acac41aac885fc6635fbd55f96ba7c845eb5e7