CXX_FAST_TLS calling convention: performance improvement for ARM.

This is the same change on ARM as r255821 on AArch64.
rdar://9001553

llvm-svn: 257424
diff --git a/llvm/lib/Target/ARM/ARMFastISel.cpp b/llvm/lib/Target/ARM/ARMFastISel.cpp
index b5f1ac4..ff2fcfa 100644
--- a/llvm/lib/Target/ARM/ARMFastISel.cpp
+++ b/llvm/lib/Target/ARM/ARMFastISel.cpp
@@ -2083,6 +2083,9 @@
   if (!FuncInfo.CanLowerReturn)
     return false;
 
+  if (TLI.supportSplitCSR(FuncInfo.MF))
+    return false;
+
   // Build a list of return value registers.
   SmallVector<unsigned, 4> RetRegs;