Mark clang-scan-deps test as requiring thread support

Otherwise the test calls a pure virtual method and crashes. Perhaps this
could be improved.

llvm-svn: 368354

clang/test/ClangScanDeps/regular_cdb.cpp

@@ -1,3 +1,4 @@
+// REQUIRES: thread_support
 // RUN: rm -rf %t.dir
 // RUN: rm -rf %t.cdb
 // RUN: mkdir -p %t.dir