Move Clang distributed thin-lto CodeGen tests into their own directory

These tests all deal with distributed thin-lto, and while their names
indicate this, it is easier to find them in a common directory.

Author: Nuri Amari

clang/test/CodeGen/thinlto-distributed-backend-skip.ll renamed to clang/test/CodeGen/distributed-thin-lto/thinlto-distributed-backend-skip.ll

@@ -6,7 +6,7 @@
 ; RUN: opt -thinlto-bc -o %t.o %s
 
 ; RUN: %clang_cc1 -triple x86_64-grtev4-linux-gnu \
-; RUN:   -fthinlto-index=%S/Inputs/thinlto-distributed-backend-skip.bc \
+; RUN:   -fthinlto-index=%S/../Inputs/thinlto-distributed-backend-skip.bc \
 ; RUN:   -emit-llvm -o - -x ir %t.o | FileCheck %s
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"