instcombine: Migrate math library call simplifications

This patch migrates the math library call simplifications from the
simplify-libcalls pass into the instcombine library call simplifier.

I have typically migrated just one simplifier at a time, but the math
simplifiers are interdependent because:

   1. CosOpt, PowOpt, and Exp2Opt all depend on UnaryDoubleFPOpt.
   2. CosOpt, PowOpt, Exp2Opt, and UnaryDoubleFPOpt all depend on
      the option -enable-double-float-shrink.

These two factors made migrating each of these simplifiers individually
more of a pain than it would be worth.  So, I migrated them all together.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167815 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Transforms/Utils/SimplifyLibCalls.h

@@ -31,7 +31,8 @@ namespace llvm {
     /// simplifier.
     LibCallSimplifierImpl *Impl;
   public:
-    LibCallSimplifier(const DataLayout *TD, const TargetLibraryInfo *TLI);
+    LibCallSimplifier(const DataLayout *TD, const TargetLibraryInfo *TLI,
+                      bool UnsafeFPShrink);
     virtual ~LibCallSimplifier();
 
     /// optimizeCall - Take the given call instruction and return a more