Update for LLVM API change

Use the new getObjectFormat/setObjectFormat instead of Environment now that the
file format is a separate field.

llvm-svn: 203161
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index ba53db0..382f8af 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1971,7 +1971,7 @@
         TC = new toolchains::Generic_ELF(*this, Target, Args);
         break;
       }
-      if (Target.getEnvironment() == llvm::Triple::MachO) {
+      if (Target.getObjectFormat() == llvm::Triple::MachO) {
         TC = new toolchains::MachO(*this, Target, Args);
         break;
       }