[dsymutil] Fix -arch option for thumb variants.

r267249 removed the dual ARM/Thumb interface from MachOObjectFile,
simplifying llvm-dsymutil's code. This unfortunately also regressed
llvm-dsymutil's ability to select thumb slices, because the simplified
code was also dealing with the discrepency between the slice arch
(eg. armv7m) and the triple arch name (eg. thumbv7m).

llvm-svn: 268894
diff --git a/llvm/tools/dsymutil/MachODebugMapParser.cpp b/llvm/tools/dsymutil/MachODebugMapParser.cpp
index 476ac80..2221520 100644
--- a/llvm/tools/dsymutil/MachODebugMapParser.cpp
+++ b/llvm/tools/dsymutil/MachODebugMapParser.cpp
@@ -294,7 +294,11 @@
       std::find(Archs.begin(), Archs.end(), "arm") != Archs.end())
     return true;
 
-  return std::find(Archs.begin(), Archs.end(), Arch) != Archs.end();
+  SmallString<16> ArchName = Arch;
+  if (Arch.startswith("thumb"))
+    ArchName = ("arm" + Arch.substr(5)).str();
+
+  return std::find(Archs.begin(), Archs.end(), ArchName) != Archs.end();
 }
 
 bool MachODebugMapParser::dumpStab() {