[Triple] Add isThumb and isARM functions.

Summary:
isThumb returns true for Thumb triples (little and big endian), isARM
returns true for ARM triples (little and big endian).
There are a few more checks using arm/thumb that are not covered by
those functions, e.g. that the architecture is either ARM or Thumb
(little endian) or ARM/Thumb little endian only.

Reviewers: javed.absar, rengolin, kristof.beyls, t.p.northover

Reviewed By: rengolin

Subscribers: llvm-commits, aemerson

Differential Revision: https://reviews.llvm.org/D34682

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310781 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Object/ELFObjectFile.cpp

@@ -260,8 +260,7 @@ void ELFObjectFileBase::setARMSubArch(Triple &TheTriple) const {
 
   std::string Triple;
   // Default to ARM, but use the triple if it's been set.
-  if (TheTriple.getArch() == Triple::thumb ||
-      TheTriple.getArch() == Triple::thumbeb)
+  if (TheTriple.isThumb())
     Triple = "thumb";
   else
     Triple = "arm";