ARM: fix mismatch between Clang and backend on exception type.

"-arch armv7k" is only normally used with a watchos target, but Clang doesn't
stop you from giving a "-miphoneos-version-min" option too, converting the
triple to "thumbv7k-apple-ios". In this case the backend will decide to use
SjLj exceptions, so Clang needs to agree so it can create the correct
predefines.

Fortunately, there's a handy function to make the decision for us now.

llvm-svn: 253355
diff --git a/clang/lib/Driver/ToolChains.cpp b/clang/lib/Driver/ToolChains.cpp
index d1ce3f4..ed22321 100644
--- a/clang/lib/Driver/ToolChains.cpp
+++ b/clang/lib/Driver/ToolChains.cpp
@@ -1053,12 +1053,8 @@
       getTriple().getArch() != llvm::Triple::thumb)
     return false;
 
-  // We can't check directly for watchOS here. ComputeLLVMTriple only
-  // fills in the ArchName correctly.
-  llvm::Triple Triple(ComputeLLVMTriple(Args));
-  return !(Triple.getArchName() == "armv7k" ||
-           Triple.getArchName() == "thumbv7k");
-
+  // Only watchOS uses the new DWARF/Compact unwinding method.
+  return !isTargetWatchOS();
 }
 
 bool MachO::isPICDefault() const { return true; }