musl: mips64: Use special MIPS definition of stack_t

stack_t is sigaltstack, which in musl has a special definition for MIPS
that switches around ss_size and ss_flags.

The 32-bit definition was already correct.

See:
https://git.musl-libc.org/cgit/musl/tree/arch/mips64/bits/signal.h#n67

Signed-off-by: Jens Reidel <adrian@travitia.xyz>

Author: Gelbpunkt

src/unix/linux_like/linux/musl/b64/mips64.rs

@@ -56,6 +56,12 @@ s! {
         __pad5: [c_int; 14],
     }
 
+    pub struct stack_t {
+        pub ss_sp: *mut c_void,
+        pub ss_size: size_t,
+        pub ss_flags: c_int,
+    }
+
     pub struct ipc_perm {
         #[cfg(musl_v1_2_3)]
         pub __key: crate::key_t,

src/unix/linux_like/linux/musl/b64/mod.rs

@@ -3,6 +3,8 @@ use crate::prelude::*;
 pub type regoff_t = c_long;
 
 s! {
+    // MIPS implementation is special, see the subfolder.
+    #[cfg(not(target_arch = "mips64"))]
     pub struct stack_t {
         pub ss_sp: *mut c_void,
         pub ss_flags: c_int,