syscall overhaul part two - unify public and internal syscall interface

with this patch, the syscallN() functions are no longer needed; a
variadic syscall() macro allows syscalls with anywhere from 0 to 6
arguments to be made with a single macro name. also, manually casting
each non-integer argument with (long) is no longer necessary; the
casts are hidden in the macros.

some source files which depended on being able to define the old macro
SYSCALL_RETURNS_ERRNO have been modified to directly use __syscall()
instead of syscall(). references to SYSCALL_SIGSET_SIZE and SYSCALL_LL
have also been changed.

x86_64 has not been tested, and may need a follow-up commit to fix any
minor bugs/oversights.

src/time/time.c

@@ -1,4 +1,3 @@
-#define SYSCALL_RETURN_ERRNO
 #include <time.h>
 #include <sys/time.h>
 #include "syscall.h"
@@ -6,7 +5,7 @@
 time_t time(time_t *t)
 {
 	struct timeval tv;
-	syscall2(__NR_gettimeofday, (long)&tv, 0);
+	__syscall(__NR_gettimeofday, &tv, 0);
 	if (t) *t = tv.tv_sec;
 	return tv.tv_sec;
 }