[ARM] Define a subtarget feature that is used to avoid using movt/movw
pairs for 32-bit immediates.

This change is needed to avoid emitting movt/movw pairs when doing LTO
and do so on a per-function basis.

Out-of-tree projects currently using cl::opt option -arm-use-movt=0 or
false to avoid emitting movt/movw pairs should make changes to add
subtarget feature "+no-movt" (see the changes made to clang in r242368).

rdar://problem/21529937

Differential Revision: http://reviews.llvm.org/D11026

llvm-svn: 242369
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.h b/llvm/lib/Target/ARM/ARMSubtarget.h
index dd101df..7542589 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.h
+++ b/llvm/lib/Target/ARM/ARMSubtarget.h
@@ -112,9 +112,9 @@
   /// IsR9Reserved - True if R9 is a not available as general purpose register.
   bool IsR9Reserved;
 
-  /// UseMovt - True if MOVT / MOVW pairs are used for materialization of 32-bit
-  /// imms (including global addresses).
-  bool UseMovt;
+  /// NoMovt - True if MOVT / MOVW pairs are not used for materialization of
+  /// 32-bit imms (including global addresses).
+  bool NoMovt;
 
   /// SupportsTailCall - True if the OS supports tail call. The dynamic linker
   /// must be able to synthesize call stubs for interworking between ARM and