round zero-byte .zerofill directives up to 1 byte.  This
should fix some "g++.dg-struct-layout-1" failures, 
rdar://7886017


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@102421 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 31cb0ca..f000a70 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -283,6 +283,8 @@
   // Handle the zerofill directive on darwin, which is a special form of BSS
   // emission.
   if (GVKind.isBSSExtern() && MAI->hasMachoZeroFillDirective()) {
+    if (Size == 0) Size = 1;  // zerofill of 0 bytes is undefined.
+    
     // .globl _foo
     OutStreamer.EmitSymbolAttribute(GVSym, MCSA_Global);
     // .zerofill __DATA, __common, _foo, 400, 5