libposix: deep refactor; add sys/posixly command

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

qa/lib/newlib/215-sigprocmask.c

@@ -0,0 +1,38 @@
+#include <signal.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/wait.h>
+
+sigset_t parent_mask;
+
+int
+main()
+{
+	int status;
+	sigset_t mask;
+
+	sigprocmask(SIG_BLOCK, NULL, &parent_mask);
+	sigaddset(&parent_mask, SIGSEGV);
+	sigprocmask(SIG_BLOCK, &parent_mask, NULL);
+	printf("SIGSEGV blocked in parent. Forking...\n");
+
+	switch(fork()){
+	case -1:
+		exit(1);
+	case 0:
+		sigprocmask(SIG_BLOCK, NULL, &mask);
+		printf("Is SIGSEGV (%llx) a member of %llx?\n", 1ULL<<(SIGSEGV-1), (long long unsigned int)mask);
+		if(sigismember(&mask, SIGSEGV) != 1){
+			printf("FAIL: SIGSEGV is not present in child's mask after fork\n");
+			exit(2);
+		}
+		printf("PASS\n");
+		exit(0);
+	default:
+		wait(&status);
+		status = WEXITSTATUS(status);
+		exit(status);
+	}
+	
+}