[ARM] Rename HW div feature to HW div Thumb. NFCI.

The hardware div feature refers only to Thumb, but because of its name
it is tempting to use it to check for hardware division in general,
which may cause problems in ARM mode. See https://reviews.llvm.org/D32005.

This patch adds "Thumb" to its name, to make its scope clear. One
notable place where I haven't made the change is in the feature flag
(used with -mattr), which is still hwdiv. Changing it would also require
changes in a lot of tests, including clang tests, and it doesn't seem
like it's worth the effort.

Differential Revision: https://reviews.llvm.org/D32160

llvm-svn: 300827
diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index 01e062b..e9bc7db 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -1702,7 +1702,8 @@
   // If we have integer div support we should have selected this automagically.
   // In case we have a real miss go ahead and return false and we'll pick
   // it up later.
-  if (Subtarget->hasDivide()) return false;
+  if (Subtarget->hasDivideInThumbMode())
+    return false;
 
   // Otherwise emit a libcall.
   RTLIB::Libcall LC = RTLIB::UNKNOWN_LIBCALL;