linux_like: mips64: Fix SI_TIMER, SI_MESGQ and SI_ASYNCIO definitions

mips64 uses the same definitions for these as the 32-bit targets. See
e.g.:

https://github.com/torvalds/linux/blob/master/arch/mips/include/uapi/asm/siginfo.h#L21
https://git.musl-libc.org/cgit/musl/tree/arch/mips64/bits/signal.h#n96

Signed-off-by: Jens Reidel <[email protected]>

(backport <#4529>)
(cherry picked from commit dff820c)

Author: Gelbpunkt

src/unix/linux_like/mod.rs

@@ -1269,7 +1269,11 @@ pub const SI_USER: c_int = 0;
 pub const SI_KERNEL: c_int = 0x80;
 pub const SI_QUEUE: c_int = -1;
 cfg_if! {
-    if #[cfg(not(any(target_arch = "mips", target_arch = "mips32r6")))] {
+    if #[cfg(not(any(
+        target_arch = "mips",
+        target_arch = "mips32r6",
+        target_arch = "mips64"
+    )))] {
         pub const SI_TIMER: c_int = -2;
         pub const SI_MESGQ: c_int = -3;
         pub const SI_ASYNCIO: c_int = -4;