run_python, run_python_compiler could readlink -f

Please include the following in your bug report:

**Version of emscripten/emsdk:**
6.0.1

**Failing command line in full:**
When installing to /usr/local/bin/emcc the emcc file created by create_entry_point,
it will fail, because it tries to find $0.py, which resolves to
`/usr/local/bin/emcc.py`, which doesn't exist.

Replacing by `readlink -f $0` would make distributors life a bit easier.

Thanks for considering.
```
--- a/tools/maint/run_python.sh
+++ b/tools/maint/run_python.sh
@@ -30,4 +30,4 @@
exit 1
fi

-exec "$_EM_PY" -E "$0.py" "$@"
+exec "$_EM_PY" -E "$(readlink -f $0).py" "$@"
--- a/tools/maint/run_python_compiler.sh
+++ b/tools/maint/run_python_compiler.sh
@@ -31,7 +31,7 @@
fi

if [ -z "$_EMCC_CCACHE" ]; then
- exec "$_EM_PY" -E "$0.py" "$@"
+ exec "$_EM_PY" -E "$(readlink -f $0).py" "$@"
else
unset _EMCC_CCACHE
exec ccache "$0" "$@"
```