Implement unique sections with an unique ID.

This allows the compiler/assembly programmer to switch back to a
section. This in turn fixes the bootstrap failure on powerpc (tested
on gcc110) without changing the ppc codegen at all.

I will try to cleanup the various getELFSection overloads in a  followup patch.
Just using a default argument now would lead to ambiguities.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234099 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCSectionELF.cpp

@@ -24,7 +24,7 @@ MCSectionELF::~MCSectionELF() {} // anchor.
 bool MCSectionELF::ShouldOmitSectionDirective(StringRef Name,
                                               const MCAsmInfo &MAI) const {
 
-  if (Unique)
+  if (isUnique())
     return false;
 
   // FIXME: Does .section .bss/.data/.text work everywhere??
@@ -148,8 +148,8 @@ void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI,
     OS << ",comdat";
   }
 
-  if (Unique)
-    OS << ",unique";
+  if (isUnique())
+    OS << ",unique " << UniqueID;
 
   OS << '\n';