[bootstrap] Honor EMSDK_NODE in bootstrap.py

[sbc100]

When EMSDK_NODE is present in the environment, prepend its directory to PATH before running bootstrap actions.

By default, emsdk avoids prepending its own node binary to PATH if a system node is already present in PATH. However, bootstrap actions (such as npm ci) may fail if the system node is an older incompatible version or lacks npm.

See: #27614

[kripken]

I don't follow, why are bootstrap actions special? That is, the same reasoning suggests this could help non-bootstrap situations too?

[sbc100]

I don't follow, why are bootstrap actions special? That is, the same reasoning suggests this could help non-bootstrap situations too?

I tried to explain the comment but maybe its not clear. Non-bootstrap tools get NODE_JS from the config file. In this case we likely don't have a config file (See the comment at the top of bootstrap.py about why we cannot include shared.py) so we are using node (npm) form the PATH instead.

However, we do really want to use the same version of node that we have in the config file when we run npm ci since that is the version of node that we end up using the node_modules directory here in the emscripten directory.

[sbc100]

Sorry, the auto-merge landed before you got a change to approve @kripken