Fix a bit of confusion about .set and produce more readable assembly.

Every target we support has support for assembly that looks like

a = b - c
.long a

What is special about MachO is that the above combination suppresses the
production of a relocation.

With this change we avoid producing the intermediary labels when they don't
add any value.

llvm-svn: 220256
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 39281c8..fc3662e 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -264,7 +264,8 @@
     Expr = MCBinaryExpr::CreateSub(Expr,
                             MCSymbolRefExpr::Create(MF.getPICBaseSymbol(), Ctx),
                                    Ctx);
-    if (MO.isJTI() && MAI.hasSetDirective()) {
+    if (MO.isJTI()) {
+      assert(MAI.doesSetDirectiveSuppressesReloc());
       // If .set directive is supported, use it to reduce the number of
       // relocations the assembler will generate for differences between
       // local labels. This is only safe when the symbols are in the same