tools/cmake: fix typo in parallel make patch

tools/cmake: fix typo in parallel make patch

The variable in the case argument was mistyped, so the case always
checked against an empty string and never matched.

Fix the variable name. Add a PKG_RELEASE to Makefile so we can bump it.

Fixes: d6de31310cc1 ("cmake: restore parallel build support for bootstrap")
Signed-off-by: Piotr Stefaniak <pstef@freebsd.org>
[add commit message, add PKG_RELEASE, fix commit title, add Fixes:]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
(cherry picked from commit e27fbae63c3436ce5588ca06b78ea88c7a316fee)