Update lldb to track recent Triple arm64 enum removal and collapse into aarch64.

See the following llvm change for details:

r213743 | tnorthover | 2014-07-23 05:32:47 -0700 (Wed, 23 Jul 2014) | 9 lines
AArch64: remove arm64 triple enumerator.

This change fixes build breaks on Linux and MacOSX lldb.

llvm-svn: 213755
diff --git a/lldb/source/Target/Thread.cpp b/lldb/source/Target/Thread.cpp
index 3aa7fbc..a445517 100644
--- a/lldb/source/Target/Thread.cpp
+++ b/lldb/source/Target/Thread.cpp
@@ -2191,7 +2191,7 @@
             case llvm::Triple::x86_64:
             case llvm::Triple::x86:
             case llvm::Triple::arm:
-            case llvm::Triple::arm64:
+            case llvm::Triple::aarch64:
             case llvm::Triple::thumb:
             case llvm::Triple::mips64:
             case llvm::Triple::hexagon: