musl: Unify definitions of siginfo_t

Musl provides a single definition for `siginfo_t` [1] with the order of
`si_code` and `si_errno` controlled by `__SI_SWAP_ERRNO_CODE`. This is
only set on mips (both 32- and 64-bit).

[1]: https://github.com/kraj/musl/blob/ffb23aef7b5339b8c3234f4c6a93c488dc873919/include/signal.h#L99-L147

[ extracted from "Remove all redundant definitions in musl backend", add
  context to the commit message - Trevor ]

(backport <rust-lang#3261>)
(cherry picked from commit e1ff5d6)

Author: bossmc

src/unix/linux_like/linux/musl/b32/arm/mod.rs

@@ -112,14 +112,6 @@ s! {
         pub f_spare: [::c_ulong; 4],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
-
     pub struct statfs64 {
         pub f_type: ::c_ulong,
         pub f_bsize: ::c_ulong,

src/unix/linux_like/linux/musl/b32/hexagon.rs

@@ -90,14 +90,6 @@ s! {
         pub f_spare: [::c_ulong; 4],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
-
     pub struct statfs64 {
         pub f_type: ::c_ulong,
         pub f_bsize: ::c_ulong,

src/unix/linux_like/linux/musl/b32/mips/mod.rs

@@ -120,14 +120,6 @@ s! {
         pub f_spare: [::c_ulong; 5],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_code: ::c_int,
-        pub si_errno: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
-
     pub struct statfs64 {
         pub f_type: ::c_ulong,
         pub f_bsize: ::c_ulong,

src/unix/linux_like/linux/musl/b32/powerpc.rs

@@ -112,14 +112,6 @@ s! {
         pub f_spare: [::c_ulong; 4],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
-
     pub struct statfs64 {
         pub f_type: ::c_ulong,
         pub f_bsize: ::c_ulong,

src/unix/linux_like/linux/musl/b32/riscv32/mod.rs

@@ -113,21 +113,6 @@ s! {
         __f_spare: [::c_int; 6],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        #[doc(hidden)]
-        #[deprecated(
-            since = "0.2.54",
-            note = "Please leave a comment on \
-                  https://github.com/rust-lang/libc/pull/1316 if you're using \
-                  this field"
-        )]
-        pub _pad: [::c_int; 29],
-        _align: [u64; 0],
-    }
-
     pub struct stack_t {
         pub ss_sp: *mut ::c_void,
         pub ss_flags: ::c_int,

src/unix/linux_like/linux/musl/b32/x86/mod.rs

@@ -116,14 +116,6 @@ s! {
         pub f_spare: [::c_ulong; 4],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
-
     pub struct statfs64 {
         pub f_type: ::c_ulong,
         pub f_bsize: ::c_ulong,

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

@@ -120,14 +120,6 @@ s! {
     pub struct sem_t {
         __val: [::c_int; 8],
     }
-
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        pub _pad: [::c_int; 29],
-        _align: [usize; 0],
-    }
 }
 
 pub const __SIZEOF_PTHREAD_RWLOCK_T: usize = 56;

src/unix/linux_like/linux/musl/b64/riscv64/mod.rs

@@ -119,21 +119,6 @@ s! {
         pub __f_spare: [::c_int; 6],
     }
 
-    pub struct siginfo_t {
-        pub si_signo: ::c_int,
-        pub si_errno: ::c_int,
-        pub si_code: ::c_int,
-        #[doc(hidden)]
-        #[deprecated(
-            since = "0.2.54",
-            note = "Please leave a comment on \
-                  https://github.com/rust-lang/libc/pull/1316 if you're using \
-                  this field"
-        )]
-        pub _pad: [::c_int; 29],
-        _align: [u64; 0],
-    }
-
     pub struct stack_t {
         pub ss_sp: *mut ::c_void,
         pub ss_flags: ::c_int,

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

@@ -144,6 +144,26 @@ s! {
         pub sa_restorer: ::Option<extern "C" fn()>,
     }
 
+    // `mips*` targets swap the `s_errno` and `s_code` fields otherwise this struct is
+    // target-agnostic (see https://www.openwall.com/lists/musl/2016/01/27/1/2)
+    pub struct siginfo_t {
+        pub si_signo: ::c_int,
+        #[cfg(not(target_arch = "mips"))]
+        pub si_errno: ::c_int,
+        pub si_code: ::c_int,
+        #[cfg(target_arch = "mips")]
+        pub si_errno: ::c_int,
+        #[doc(hidden)]
+        #[deprecated(
+            since = "0.2.54",
+            note = "Please leave a comment on \
+                  https://github.com/rust-lang/libc/pull/1316 if you're using \
+                  this field"
+        )]
+        pub _pad: [::c_int; 29],
+        _align: [usize; 0],
+    }
+
     pub struct statvfs {
         pub f_bsize: ::c_ulong,
         pub f_frsize: ::c_ulong,