[PATCH] [CFI] Require -flto instead of implying it.

[Peter Collingbourne]

LGTM

I think you will also need to adjust `config.lto_flags` in `compiler-rt/test/lit.common.cfg`.


================
Comment at: lib/Driver/Driver.cpp:1387
@@ -1390,2 +1386,3 @@
+bool Driver::IsUsingLTO(const ArgList &Args) const {
   if (Args.hasFlag(options::OPT_flto, options::OPT_fno_lto, false))
     return true;
----------------
This could just be `return Args.hasFlag(...)` now.

http://reviews.llvm.org/D10560

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