Add a lit reproducer for PR37091

[dstenb]

Summary

This adds a lit reproducer that verifies that no temporary
assembly files are left behind when using clang-tidy with a
target that does not support the internal assembler.

The fix is in Tooling (https://reviews.llvm.org/D45686), but
as we need to verify that no files are left behind, it is
probably easier and better to create a lit reproducer for a
specific tool here instead of creating a unit test.

[dstenb]

Merged into D45686.

test/clang-tidy/pr37091.cpp

+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+
+// This is a reproducer for PR37091.
+//
+// Verify that no temporary files are left behind by the clang-tidy invocation.
+
+// RUN: env TMPDIR=%t TEMP=%t TMP=%t clang-tidy %s -- --target=mips64
+// RUN: rmdir %t