Reset registers to their 'initial' state instead of a semi-random
pattern in write tests.  While the latter might have been helpful
while debugging failures (i.e. to distinguish unmodified registers
from mistakenly written zeroes), the former makes it possible to test
whether xstate_bv field is written correctly when using XSAVE.

With this change, the four relevant tests start failing on NetBSD
without D90105.

Differential Revision: https://reviews.llvm.org/D90114

The original patch got reverted because it broke `check-lldb` on a clean
build. This fixes that.

llvm-svn: 374201

as it appears to have broken check-lldb.

This reverts r374184 (git commit 22314179f0660c172514b397060fd8f34b586e82)

llvm-svn: 374187

LLDB has three major testing strategies: unit tests, tests that exercise
the SB API though dotest.py and what we currently call lit tests. The
later is rather confusing as we're now using lit as the driver for all
three types of tests. As most of this grew organically, the directory
structure in the LLDB repository doesn't really make this clear.

The 'lit' tests are part of the root and among these tests there's a
Unit and Suite folder for the unit and dotest-tests. This layout makes
it impossible to run just the lit tests.

This patch changes the directory layout to match the 3 testing
strategies, each with their own directory and their own configuration
file. This means there are now 3 directories under lit with 3
corresponding targets:

 - API (check-lldb-api): Test exercising the SB API.
 - Shell (check-lldb-shell): Test exercising command line utilities.
 - Unit (check-lldb-unit): Unit tests.

Finally, there's still the `check-lldb` target that runs all three test
suites.

Finally, this also renames the lit folder to `test` to match the LLVM
repository layout.

Differential revision: https://reviews.llvm.org/D68606

llvm-svn: 374184