Add initial support for 'goto' statements.

ispc now supports goto, but only under uniform control flow--i.e.
it must be possible for the compiler to statically determine that
all program instances will follow the goto.  An error is issued at
compile time if a goto is used when this is not the case.

cbackend.cpp

@@ -376,7 +376,7 @@ namespace {
       if (I.getType() == Type::getVoidTy(I.getContext()) || !I.hasOneUse() ||
           isa<TerminatorInst>(I) || isa<CallInst>(I) || isa<PHINode>(I) ||
           isa<LoadInst>(I) || isa<VAArgInst>(I) || isa<InsertElementInst>(I) ||
-          isa<InsertValueInst>(I) || isa<ExtractValueInst>(I))
+          isa<InsertValueInst>(I) || isa<ExtractValueInst>(I) || isa<SelectInst>(I))
         // Don't inline a load across a store or other bad things!
         return false;