gdbsupport: make gdb::parallel_for_each's n parameter a template parameter

This value will likely never change at runtime, so we might as well make
it a template parameter.  This has the "advantage" of being able to
remove the unnecessary param from gdb::sequential_for_each.

Change-Id: Ia172ab8e08964e30d4e3378a95ccfa782abce674
Approved-By: Tom Tromey <tom@tromey.com>
3 files changed