Always use kernel_timespec as timespec

The `timespec` structure is now defined to be the `__kernel_timespec`
type, and all syscalls/ABI definitions that reference `timespec` withh
either be modified to work or be altered to return a timespec from
existing time components - see the new `makeTimespec` function for how
this is done.

lib/std/os/linux.zig

@@ -7541,15 +7541,22 @@ pub const POSIX_FADV = switch (native_arch) {
 };
 
 /// The timespec struct used by the kernel.
-pub const kernel_timespec = extern struct {
+pub const timespec = extern struct {
+    /// Seconds.
     sec: i64,
+    /// Nanoseconds.
     nsec: i64,
-};
 
-// https://github.com/ziglang/zig/issues/4726#issuecomment-2190337877
-pub const timespec = if (native_arch == .riscv32) kernel_timespec else extern struct {
-    sec: isize,
-    nsec: isize,
+    pub fn makeTimespec(sec: anytype, nsec: anytype) timespec {
+        comptime {
+            const si = @typeInfo(@TypeOf(sec));
+            assert(si == .int and (si.int.bits == 32 or si.int.bits == 64));
+            const nsi = @typeInfo(@TypeOf(sec));
+            assert(nsi == .int and (nsi.int.bits == 32 or nsi.int.bits == 64));
+        }
+
+        return .{ .sec = @intCast(sec), .nsec = @intCast(nsec) };
+    }
 };
 
 pub const XDP = struct {