Fix problems in libbacktrace.

- Add a wait for stop to backtrace_test. There is a possible race
  condition that is exposed when using libunwind.
- Fix a few calls to unwind function calls.

Bug: 8410085
Change-Id: I7487d687f6d4b7b05b8a96ad1c5f7183681e5c95

Conflicts:

	libbacktrace/backtrace_test.c
	libbacktrace/unwind_local.c
	libbacktrace/unwind_remote.c
Handle screendumps for all framebuffer sizes

readx() treats a partial read as an error but also consumes the data,
Now exactly the amount of data needed for the screendump is requested.

This bug showed up for framebuffers that were not a multiple of 640
bytes.

Also fix a compiler warning related to handing pipe() failure.

Change-Id: I8b1713923e156d4e3424784152e5dc5cbc7d478d

Conflicts:

	adb/framebuffer_service.c
Only build host library on linux-x86.

Change-Id: I26d5bd4b34c3669897fea1488fa58972f4299757

Conflicts:

	libbacktrace/Android.mk
Expose /dev/hw_random to group "system".

This is needed to let EntropyMixer (runs inside system_server) read
from /dev/hw_random.

Change-Id: Ifde851004301ffd41b2189151a64a0c5989c630f
Set security context of /adb_keys and /data/misc/adb/adb_keys.

I97b3d86a69681330bba549491a2fb39df6cf20ef introduced a separate type
for the adb_keys file.  Set the security context of the adb_keys file
accordingly by adding restorecon commands to init.rc.

Change-Id: I30e4d2a1ae223a03eadee58a883c79932fff59fe
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Update debuggerd to use libbacktrace.

Remove all of the code in debuggerd that uses libcorkscrew directly
and replace with libbacktrace.

Also do a bit of refactoring to clean up some functions that were
passing around variables that weren't used.

Bug: 8410085

Change-Id: I27da4fbe3f12ce38a85b4432fc1119984c9c391b