[system] align license and license banners with Fuchsia

This adjusts the Magenta userspace code to match the prevailing
license in Fuchsia (three-clause BSD), using the same banner
and license text.

Change-Id: I6b6d79435c5dbaa32027888874849e4f47aaa7be

[system][utest]/[mxsh] Make runtests output less by default

To output the full amount use "runtests -v".

This introduces a verbosity_level concept for system/ulib/unnittest
with unittest_set_verbosity_level(level) to control it.

Change-Id: I0f301adf4fdac9a3cf6c76e41d4b9587c9495d1f

[ulib][unittest] Move unittest into its own library

Change-Id: I1586278e3bbb6ceacd26a1342985922dc8861cf7

[build][userspace] Support .init_array for userspace with gcc

In particular, with this change, C++ constructors are running now, and
static C variables are initialized.

Change-Id: If0252773faae705af78902f782aaa200d0c5f85e

[utests] Convert qsort test to unittest framework

Change-Id: I301ea928c6d12d4612b97e441994f89833b829b5

[utest] Remove some useless test spam

Change-Id: Ib0b0529ddd10c5dc331043ec0b2381690806f3ee

[musl] Reintroduce qsort.c and a test for it

I erred on the side of caution in the initial open sourcing. This file
is ok but did need to be moved to third_party.

Change-Id: I86abf8634e4f227fe2220eda7928fab4860dd436