Ignored `ccache` directory. (#4912)

Co-authored-by: Daniel McIlvaney <damcilva@microsoft.com>

.gitignore

@@ -62,6 +62,9 @@ build/
 [Ll]ogs/
 out/
 
+# Builds may generate a CCache directory.
+ccache/
+
 # Visual Studio 2015/2017 cache/options directory
 .vs/
 # Uncomment if you have tasks that create the project's static files in wwwroot