Bug 1461714 - Run node in export; r=ochameau,nalexander

In bug 1461714 we run node.py to generate main.js in the objdir, and use
FINAL_TARGET_FILES to install it into dist. However, when both rules are
run in parallel in the misc tier, the install target may pick up the
main.js file from the srcdir via VPATH, so we end up with the wrong file
in dist. This causes some mochitests to fail with "uncaught exception -
SyntaxError: import declarations may only appear at top level of a
module at
@resource://devtools/client/debugger/new/src/main.js:7:undefined"

The workaround here is to run these node.py invocations (which always
write to node.stub) in the export tier, so that when the install target
in misc is processed, the objdir version of the file is always present
and takes precedence.

A better fix would probably be to remove our reliance on VPATH, and just
pass in the path to files in the srcdir when they are required. That
could potentially be a major overhaul, however.

MozReview-Commit-ID: JZ04C7zJPbX

Differential Revision: https://phabricator.services.mozilla.com/D7770

--HG--
extra : moz-landing-system : lando

python/mozbuild/mozbuild/frontend/data.py

@@ -1170,6 +1170,7 @@ class GeneratedFile(ContextDerived):
             '.inc',
             '.py',
             '.rs',
+            'node.stub', # To avoid VPATH issues with installing node files: https://bugzilla.mozilla.org/show_bug.cgi?id=1461714#c55
         )
         self.required_for_compile = [f for f in self.outputs if f.endswith(suffixes) or 'stl_wrappers/' in f]