Make signal handling work well across platforms

- Fix sigsuspend() on XNU
- Fix strsignal() on non-Linux
- Add unit tests for strsignal()
- Add unit tests for setitimer()
- Add unit tests for sigsuspend()
- Rewrite setitimer() for New Technology
- Rewrite nanosleep() for New Technology
- Polyfill SIGALRM on the New Technology
- select(0,0,0,0) on NT now calls pause()
- Remove some NTDLL calls that aren't needed
- Polyfill SA_NOCLDWAIT on the New Technology
- Polyfill SA_RESETHAND on the New Technology
- Polyfill sigprocmask() on the New Technology
- Polyfill SIGCHLD+SIG_IGN on the New Technology
- Polyfill SA_RESTART masking on the New Technology
- Deliver console signals from main thread on New Technology
- Document SA_RESTART behavior w/ @sarestartable / @norestart
- System call trace in MODE=dbg now prints inherited FDs and signal mask

libc/nt/kernel32/CreateThread.s

@@ -2,11 +2,11 @@
 .imp	kernel32,__imp_CreateThread,CreateThread,0
 
 	.text.windows
-CreateThread:
+__CreateThread:
 	push	%rbp
 	mov	%rsp,%rbp
 	.profilable
 	mov	__imp_CreateThread(%rip),%rax
 	jmp	__sysv2nt6
-	.endfn	CreateThread,globl
+	.endfn	__CreateThread,globl
 	.previous

libc/nt/master.sh

@@ -685,7 +685,7 @@ imp	'CreateSymbolicLinkTransactedA'				CreateSymbolicLinkTransactedA				kernel32
 imp	'CreateSymbolicLinkTransacted'				CreateSymbolicLinkTransactedW				kernel32	238
 imp	'CreateSystemThreads'					CreateSystemThreads					user32		1623
 imp	'CreateTapePartition'					CreateTapePartition					kernel32	240
-imp	'CreateThread'						CreateThread						kernel32	0	6	# KernelBase
+imp	'__CreateThread'					CreateThread						kernel32	0	6	# KernelBase
 imp	'CreateThreadpool'					CreateThreadpool					kernel32	0		# KernelBase
 imp	'CreateThreadpoolCleanupGroup'				CreateThreadpoolCleanupGroup				kernel32	0		# KernelBase
 imp	'CreateThreadpoolIo'					CreateThreadpoolIo					kernel32	0		# KernelBase