MFC r329794, r329801 (by emaste@):

Correct proper nouns in the Linuxulator

- Capitalize Linux
- Spell FreeBSD out in full
- Address some style(9) on changed lines

Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

MFC r329370, r330239: Rationalize license text on Linuxolator files

Many licenses on Linuxolator files contained small variations from the
standard FreeBSD license text. To avoid license proliferation switch to
the standard 2-clause FreeBSD license for those files where I have
permission from each of the listed copyright holders.

Approved by: dchagin, kan, marcel, rdivacky, sos
Sponsored by: The FreeBSD Foundation

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

MFC r313154:
For i386, remove config options CPU_DISABLE_CMPXCHG, CPU_DISABLE_SSE
and device npx.

MFC 302900,302902,302921,303461,304009:
Add a mask of optional ptrace() events.

302900:
Add a test for user signal delivery.

This test verifies we get the correct ptrace event details when a signal
is posted to a traced process from userland.

302902:
Add a mask of optional ptrace() events.

ptrace() now stores a mask of optional events in p_ptevents. Currently
this mask is a single integer, but it can be expanded into an array of
integers in the future.

Two new ptrace requests can be used to manipulate the event mask:
PT_GET_EVENT_MASK fetches the current event mask and PT_SET_EVENT_MASK
sets the current event mask.

The current set of events include:
- PTRACE_EXEC: trace calls to execve().
- PTRACE_SCE: trace system call entries.
- PTRACE_SCX: trace syscam call exits.
- PTRACE_FORK: trace forks and auto-attach to new child processes.
- PTRACE_LWP: trace LWP events.

The S_PT_SCX and S_PT_SCE events in the procfs p_stops flags have
been replaced by PTRACE_SCE and PTRACE_SCX. PTRACE_FORK replaces
P_FOLLOW_FORK and PTRACE_LWP replaces P2_LWP_EVENTS.

The PT_FOLLOW_FORK and PT_LWP_EVENTS ptrace requests remain for
compatibility but now simply toggle corresponding flags in the
event mask.

While here, document that PT_SYSCALL, PT_TO_SCE, and PT_TO_SCX both
modify the event mask and continue the traced process.

302921:
Rename PTRACE_SYSCALL to LINUX_PTRACE_SYSCALL.

303461:
Note that not all optional ptrace events use SIGTRAP.

New child processes attached due to PTRACE_FORK use SIGSTOP instead of
SIGTRAP. All other ptrace events use SIGTRAP.

304009:
Remove description of P_FOLLOWFORK as this flag was removed.