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
Enabling the lto property for a module builds that module and all static
dependencies with LTO.
LTO (link-time optimization) allows the compiler to optimize and
generate code for the entire module at link time, rather than
per-compilation unit. LTO is required for Clang CFI and other
whole-program optimization techniques. LTO also allows cross-compilation
unit optimizations that should result in faster and smaller code, at the
expense of additional compilation time.
Test: make -j12 libc with lto: true for libc
Change-Id: Ib8baefedf60e02701d44673a7c473e0845730101
