Add more generated files to .gitconfig (#490)

Two of these are ones that occur with --embedded users.

fastcomp-clang exists when users build fastcomp from source.

.gitignore

@@ -3,9 +3,11 @@ __pycache__
 
 # Support for --embedded configs
 /.emscripten
+/.emscripten.old
 /.emscripten_cache
 /.emscripten_cache__last_clear
 /.emscripten_sanity
+/.emscripten_sanity_wasm
 
 # Auto-generated by `active`
 /emsdk_set_env.bat
@@ -18,6 +20,7 @@ __pycache__
 /gnu
 /upstream
 /fastcomp
+/fastcomp-clang/
 /llvm
 /releases
 /clang