init.sh: put TMPDIR inside xbmkpwd, not /tmp

This way, all operations will be done inside the xbmk
work directory. This is being done, so that I can then
reliably sandybox certain commands in future commits,
for example the "rm" command.

This will also allow me to unify the location of all
temporary files, in future commits. I previously used
the /tmp directory because it's tmpfs-based on many
setups, and this is great for performance. However, in
practise, I never noticed any difference in performance
when benchmarking it (testing /tmp on-disk versus tmpfs).

Signed-off-by: Leah Rowe <leah@libreboot.org>

.gitignore

@@ -44,3 +44,4 @@
 /r
 /e
 /xbmkpath/
+/xbmkwd/