setitimer, getitimer: decouple time_t from long

these functions have no new time64 syscall, so the existence of a
time64 syscall cannot be used as the condition for the new code.
instead, assume the syscall takes timevals as longs, which is true
everywhere but x32, and interface with the kernel through long[4]
objects.

rather than adding new hacks to special-case x32 here, just add
x32-specific source files since a trivial syscall wrapper suffices
there.

the new code paths added in this commit are statically unreachable on
all current archs, but will become reachable when 32-bit archs get
64-bit time_t.

src/signal/getitimer.c

@@ -3,5 +3,16 @@
 
 int getitimer(int which, struct itimerval *old)
 {
+	if (sizeof(time_t) > sizeof(long)) {
+		long old32[4];
+		int r = __syscall(SYS_getitimer, which, old32);
+		if (!r) {
+			old->it_interval.tv_sec = old32[0];
+			old->it_interval.tv_usec = old32[1];
+			old->it_value.tv_sec = old32[2];
+			old->it_value.tv_usec = old32[3];
+		}
+		return __syscall_ret(r);
+	}
 	return syscall(SYS_getitimer, which, old);
 }

src/signal/setitimer.c

@@ -1,7 +1,26 @@
 #include <sys/time.h>
+#include <errno.h>
 #include "syscall.h"
 
+#define IS32BIT(x) !((x)+0x80000000ULL>>32)
+
 int setitimer(int which, const struct itimerval *restrict new, struct itimerval *restrict old)
 {
+	if (sizeof(time_t) > sizeof(long)) {
+		time_t is = new->it_interval.tv_sec, vs = new->it_value.tv_sec;
+		long ius = new->it_interval.tv_usec, vus = new->it_value.tv_usec;
+		if (!IS32BIT(is) || !IS32BIT(vs))
+			return __syscall_ret(-ENOTSUP);
+		long old32[4];
+		int r = __syscall(SYS_setitimer, which,
+			((long[]){is, ius, vs, vus}), old32);
+		if (!r && old) {
+			old->it_interval.tv_sec = old32[0];
+			old->it_interval.tv_usec = old32[1];
+			old->it_value.tv_sec = old32[2];
+			old->it_value.tv_usec = old32[3];
+		}
+		return __syscall_ret(r);
+	}
 	return syscall(SYS_setitimer, which, new, old);
 }

src/signal/x32/getitimer.c

@@ -0,0 +1,7 @@
+#include <sys/time.h>
+#include "syscall.h"
+
+int getitimer(int which, struct itimerval *old)
+{
+	return syscall(SYS_getitimer, which, old);
+}

src/signal/x32/setitimer.c

@@ -0,0 +1,7 @@
+#include <sys/time.h>
+#include "syscall.h"
+
+int setitimer(int which, const struct itimerval *restrict new, struct itimerval *restrict old)
+{
+	return syscall(SYS_setitimer, which, new, old);
+}