Rename local variable to avoid confusion.

"mm" is used all over the kernel for a struct task_mm instance.
Such a struct holds information about all of a task's memory areas,
page directory, etc. This usage is entirely different, so should have
a different name.
Fix potential infinite loop in pmm_alloc_continuous.

If there wasn't enough continous free frames starting at the first free frame,
the loop should skip forwards to just after the first used frame it finds, and
start over looking there.
Instead, due to a typo, it started looking in the exact spot every time, causing
an infinite loop.
Various minor Makefile (etc.) updates