Add prototype ucontext_t support.

src/platform/linux/signal.rs

@@ -14,6 +14,48 @@ use crate::{
     },
 };
 
+// Mirrors the ucontext_t struct from the libc crate on Linux.
+#[repr(C)]
+pub struct ucontext_t {
+    pub uc_flags: c_ulong,
+    pub uc_link: *mut ucontext_t,
+    pub uc_stack: stack_t,
+    pub uc_mcontext: mcontext_t,
+    pub uc_sigmask: sigset_t,
+    __private: [u8; 512],
+}
+#[repr(C)]
+pub struct _libc_fpstate {
+    pub cwd: u16,
+    pub swd: u16,
+    pub ftw: u16,
+    pub fop: u16,
+    pub rip: u64,
+    pub rdp: u64,
+    pub mxcsr: u32,
+    pub mxcr_mask: u32,
+    pub _st: [_libc_fpxreg; 8],
+    pub _xmm: [_libc_xmmreg; 16],
+    __private: [u64; 12],
+}
+#[repr(C)]
+pub struct _libc_fpxreg {
+    pub significand: [u16; 4],
+    pub exponent: u16,
+    __private: [u16; 3],
+}
+
+#[repr(C)]
+pub struct _libc_xmmreg {
+    pub element: [u32; 4],
+}
+#[repr(C)]
+pub struct mcontext_t {
+    pub gregs: [i64; 23], // TODO: greg_t?
+    pub fpregs: *mut _libc_fpstate,
+    __private: [u64; 8],
+}
+
 impl PalSignal for Sys {
     unsafe fn getitimer(which: c_int, out: *mut itimerval) -> c_int {
         e(syscall!(GETITIMER, which, out)) as c_int