[AVR] Add the integrated testing tool to the .gitignore

We build it as an LLVM tool.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289645 91177308-0d34-0410-b5e6-96231b3b80d8

Author: Dylan McKay

.gitignore

@@ -58,6 +58,8 @@ tools/lld
 tools/llgo
 # Polly, which is tracked independently.
 tools/polly
+# avrlit, which is tracked independently.
+tools/avrlit
 # Sphinx build tree, if building in-source dir.
 docs/_build
 # VSCode config files.