relibc: add missing POSIX/Linux headers and constants

New headers:
- include/sys/ioccom.h: Linux UAPI ioctl encoding macros (_IO/_IOR/_IOW/_IOWR)
- include/byteswap.h: bswap_16/32/64 inline functions
- src/header/sys_statfs/: struct statfs + statfs()/fstatfs() functions
  (delegates to fstatvfs, converts to Linux struct statfs format)

New constants:
- sys_socket: MSG_NOSIGNAL, MSG_PROBE, MSG_CONFIRM, MSG_MORE, MSG_FASTOPEN
- sys_mman: MAP_GROWSDOWN, MAP_DENYWRITE, MAP_EXECUTABLE, MAP_LOCKED, MAP_NONBLOCK
- elf/cbindgen.toml: ELFMAG and SELFMAG #defines in after_includes

These headers eliminate the need for shim patches in libwayland (MSG_NOSIGNAL),
mesa (sys/ioccom.h), qtbase (sys/statfs.h, ELFMAG), pipewire/wireplumber
(byteswap.h, MAP_* flags).

src/header/elf/cbindgen.toml

@@ -1,4 +1,6 @@
 after_includes = """
+#define ELFMAG "\\177ELF"
+#define SELFMAG 4
 #define ELF32_ST_BIND(val)      (((unsigned char) (val)) >> 4)
 #define ELF32_ST_TYPE(val)      ((val) & 0xf)
 #define ELF32_ST_INFO(bind, type)   (((bind) << 4) + ((type) & 0xf))

src/header/mod.rs

@@ -110,6 +110,7 @@ pub mod sys_select;
 // TODO: sys/shm.h
 pub mod sys_socket;
 pub mod sys_stat;
+pub mod sys_statfs;
 pub mod sys_statvfs;
 #[allow(non_upper_case_globals)]
 pub mod sys_syscall;

src/header/sys_mman/mod.rs

@@ -34,6 +34,11 @@ pub const MAP_TYPE: c_int = 0x000F;
 pub const MAP_ANON: c_int = 0x0020;
 pub const MAP_ANONYMOUS: c_int = MAP_ANON;
 pub const MAP_STACK: c_int = 0x20000;
+pub const MAP_GROWSDOWN: c_int = 0x0100;
+pub const MAP_DENYWRITE: c_int = 0x0800;
+pub const MAP_EXECUTABLE: c_int = 0x01000;
+pub const MAP_LOCKED: c_int = 0x2000;
+pub const MAP_NONBLOCK: c_int = 0x10000;
 /// cbindgen:ignore
 pub const MAP_FAILED: *mut c_void = usize::wrapping_neg(1) as *mut c_void;
 

src/header/sys_socket/constants.rs

@@ -51,6 +51,11 @@ pub const MSG_TRUNC: c_int = 32;
 pub const MSG_DONTWAIT: c_int = 64;
 pub const MSG_WAITALL: c_int = 256;
 pub const MSG_CMSG_CLOEXEC: c_int = 0x40000000;
+pub const MSG_NOSIGNAL: c_int = 0x4000;
+pub const MSG_PROBE: c_int = 0x10;
+pub const MSG_CONFIRM: c_int = 0x800;
+pub const MSG_MORE: c_int = 0x8000;
+pub const MSG_FASTOPEN: c_int = 0x20000000;
 
 pub const IP_ADD_SOURCE_MEMBERSHIP: c_int = 70;
 pub const IP_DROP_SOURCE_MEMBERSHIP: c_int = 71;

src/header/sys_statfs/cbindgen.toml

@@ -0,0 +1,11 @@
+sys_includes = ["sys/types.h"]
+include_guard = "_SYS_STATFS_H"
+language = "C"
+style = "tag"
+usize_is_size_t = true
+
+[export]
+include = ["statfs"]
+
+[fn]
+prefix = ""

src/header/sys_statfs/mod.rs

@@ -0,0 +1,70 @@
+use crate::{
+    c_str::CStr,
+    error::ResultExt,
+    header::fcntl::O_PATH,
+    out::Out,
+    platform::{
+        Pal, Sys,
+        types::{c_char, c_int, c_long},
+    },
+};
+
+#[repr(C)]
+#[derive(Default)]
+pub struct statfs {
+    pub f_type: c_long,
+    pub f_bsize: c_long,
+    pub f_blocks: c_long,
+    pub f_bfree: c_long,
+    pub f_bavail: c_long,
+    pub f_files: c_long,
+    pub f_ffree: c_long,
+    pub f_fsid: [c_int; 2],
+    pub f_namelen: c_long,
+    pub f_frsize: c_long,
+    pub f_flags: c_long,
+    pub f_spare: [c_long; 4],
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn statfs(path: *const c_char, buf: *mut statfs) -> c_int {
+    let path = unsafe { CStr::from_ptr(path) };
+    let buf = unsafe { Out::nonnull(buf) };
+    let fd = Sys::open(path, O_PATH, 0).or_minus_one_errno();
+    if fd < 0 {
+        return -1;
+    }
+    let res = unsafe { fill_statfs(fd, buf) };
+    if let Ok(()) = Sys::close(fd) {}
+    res
+}
+
+#[unsafe(no_mangle)]
+pub unsafe extern "C" fn fstatfs(fd: c_int, buf: *mut statfs) -> c_int {
+    let buf = unsafe { Out::nonnull(buf) };
+    unsafe { fill_statfs(fd, buf) }
+}
+
+unsafe fn fill_statfs(fd: c_int, mut buf: Out<statfs>) -> c_int {
+    let mut sv = crate::header::sys_statvfs::statvfs::default();
+    let sv_out = Out::from_mut(&mut sv);
+    let res = Sys::fstatvfs(fd, sv_out);
+    if res.is_err() {
+        return res.map(|()| 0).or_minus_one_errno();
+    }
+    buf.write(statfs {
+        f_type: 0xEF53,
+        f_bsize: sv.f_bsize as c_long,
+        f_blocks: sv.f_blocks as c_long,
+        f_bfree: sv.f_bfree as c_long,
+        f_bavail: sv.f_bavail as c_long,
+        f_files: sv.f_files as c_long,
+        f_ffree: sv.f_ffree as c_long,
+        f_fsid: [sv.f_fsid as c_int, 0],
+        f_namelen: sv.f_namemax as c_long,
+        f_frsize: sv.f_frsize as c_long,
+        f_flags: sv.f_flag as c_long,
+        f_spare: [0; 4],
+    });
+    0
+}