DebugInfo: Use assembly label arithmetic for address pool size for easier reading/editing

Recommits 350048, 350050 That broke buildbots because of some typos in
the test case.

llvm-svn: 352019
diff --git a/llvm/lib/CodeGen/AsmPrinter/AddressPool.h b/llvm/lib/CodeGen/AsmPrinter/AddressPool.h
index 9ee98e5..f92cf72 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AddressPool.h
+++ b/llvm/lib/CodeGen/AsmPrinter/AddressPool.h
@@ -54,7 +54,7 @@
   void setLabel(MCSymbol *Sym) { AddressTableBaseSym = Sym; }
 
 private:
-  void emitHeader(AsmPrinter &Asm, MCSection *Section);
+  MCSymbol *emitHeader(AsmPrinter &Asm, MCSection *Section);
 
   /// Symbol designates the start of the contribution to the address table.
   MCSymbol *AddressTableBaseSym = nullptr;