ARM: Default to apcs-gnu ABI for NetBSD

r216662 changed the default ABI for 32-bit ARM targets to be "aapcs"
when no environment is given in the triple, however NetBSD requires it
to be "apcs-gnu".

llvm-svn: 217141
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index df2f9cf..2f14830 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -755,9 +755,14 @@
       break;
     case llvm::Triple::EABIHF:
     case llvm::Triple::EABI:
-    default:
       ABIName = "aapcs";
       break;
+    default:
+      if (Triple.getOS() == llvm::Triple::NetBSD)
+        ABIName = "apcs-gnu";
+      else
+        ABIName = "aapcs";
+      break;
     }
   }
   CmdArgs.push_back("-target-abi");