[PATCH] Fix for PR20104. Enable GAS compliant coprocessor register name.

[Stepan Dyatkovskiy]

Yup, Renato proposed good idea. Final patch looks fine, except tiny thing, could you use single drop_front call (see inline comments)?

================
Comment at: lib/Target/ARM/AsmParser/ARMAsmParser.cpp:3100
@@ +3099,3 @@
+    Name = Name.drop_front();
+  Name = Name.drop_front();
+
----------------
May be like this?
Name = (Name[1] == 'r') ? Name.drop_front(2) : Name.drop_front();

http://reviews.llvm.org/D4254