Do not add uwtable attribute by default for MachO targets.

r217178 changed clang to add function attribute uwtable by default on
Win64, which caused the __eh_frame section to be emitted by default.
This commit restores the previous behavior for MachO targets.

rdar://problem/25282627


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@268589 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Driver/MSVCToolChain.cpp

@@ -71,6 +71,11 @@ bool MSVCToolChain::IsUnwindTablesDefault() const {
   // Emit unwind tables by default on Win64. All non-x86_32 Windows platforms
   // such as ARM and PPC actually require unwind tables, but LLVM doesn't know
   // how to generate them yet.
+
+  // Don't emit unwind tables by default for MachO targets.
+  if (getTriple().isOSBinFormatMachO())
+    return false;
+
   return getArch() == llvm::Triple::x86_64;
 }
 

test/Driver/win-macho-unwind.c

+// RUN: %clang -target x86_64-pc-win32-macho -### -S %s -o %t.s 2>&1 | FileCheck %s
+ 
+// Do not add function attribute "uwtable" for macho targets.
+// CHECK-NOT: -munwind-tables