Change build tmp dir to support parallel builds

[e9gille]

Fixes #1322

[dyaandys]

My apologies Gil .. it should have been JOB_NAME.

Otherwise it looks fine.

[dyaandys]

Hmm .. I think the issue is that the packaging tool does not like having tmp under the top level directory .. we see errors like
Error: Cannot copy '.' to a subdirectory of itself,
in the Jenkins output. So I think we'll have to back off some of the changes while we think more about this.

Can we therefore for now alter mk:

`diff --git a/mk b/mk
index 2e54a6d2..e430ad5f 100755
--- a/mk
+++ b/mk
@@ -51,11 +51,17 @@ const incl = new RegExp('^$'
const pkg = (x, y, f) => {
const version = isDyalogBuild ? process.env.APPVERSION : v;
let tmpdir;

• if (process.env.JOB_NAME) {
• tmpdir = ${process.env.WORKSPACE}/tmp;
• } else {
• tmpdir = /tmp/ridebuild_${version}_${rq('os').userInfo().username}_${process.pid};
• }
  +// Creating tmpdir under WORKSPACE under Jenkins would be preferable, but that currently
  +// leads to errors like "Error: Cannot copy '.' to a subdirectory of itself, "
  +// so for now create tmpdir in /tmp. This code doesn't tidy up after itself so
  +// for now we'll create a per-user directory which results in just one or
  +// two tmpdirs, but avoids the permissions issues seen when using just one tmpdir
  +// if (process.env.JOB_NAME) {
  +// tmpdir = ${process.env.WORKSPACE}/tmp;
  +// } else {
  +// tmpdir = /tmp/ridebuild_${version}_${rq('os').userInfo().username}_${process.pid};
  +// }

• tmpdir = /tmp/ridebuild_${version}_${rq('os').userInfo().username};
  rq('@electron/packager')({
  dir: '.',
  platform: x,
  `