libposix: deep refactor; add sys/posixly command

With these changes, libposix (and newlib) can run MirBSD Korn Shell.

qa/lib/newlib/206-signals.c

@@ -0,0 +1,51 @@
+#include <signal.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void sigusr1() {
+	printf("Got SIGUSR1\n");
+	exit(0);
+}
+
+int
+main()
+{
+	sigset_t old_set,  new_set;
+	sigemptyset(&old_set);
+	sigemptyset(&new_set);
+
+	signal(SIGUSR1, sigusr1);
+
+	if(sigaddset(&new_set, SIGSEGV) == 0)
+	{
+		printf("sigaddset successfully added for SIGSEGV\n");
+	}
+	sigprocmask(SIG_BLOCK, &new_set, &old_set);
+
+	printf("raise(SIGSEGV)\n");
+	raise(SIGSEGV);
+
+	if(sigaddset(&new_set, SIGUSR1) == 0)
+	{
+		printf("sigaddset successfully added for SIGUSR1\n");
+	}
+	if(sigprocmask(SIG_BLOCK, &new_set, &old_set) == -1)
+	{
+		perror("sigprocmask");
+	}
+
+	printf("raise(SIGUSR1)\n");
+	raise(SIGUSR1);
+
+	sigemptyset(&new_set);
+	sigaddset(&new_set, SIGUSR1);
+
+	printf("unblock SIGUSR1 via sigprocmask\n");
+	if(sigprocmask(SIG_UNBLOCK, &new_set, &old_set) == -1)
+	{
+		perror("sigprocmask");
+	}
+
+	return 1;
+}