Fix wrong `struct ucontext_t` typedef for all arches.

The correct one is `struct ucontext` -> `ucontext_t`.

Signed-off-by: Dmitry Chestnykh <dm.chestnykh@gmail.com>

libc/sysdeps/linux/aarch64/sys/ucontext.h

@@ -45,10 +45,10 @@ typedef elf_fpregset_t	fpregset_t;
 typedef struct sigcontext mcontext_t;
 
 /* Userlevel context.  */
-typedef struct ucontext_t
+typedef struct ucontext
   {
     unsigned long uc_flags;
-    struct ucontext_t *uc_link;
+    struct ucontext *uc_link;
     stack_t uc_stack;
     __sigset_t uc_sigmask;
     unsigned char __reserved[128];

libc/sysdeps/linux/riscv64/sys/ucontext.h

@@ -83,10 +83,10 @@ typedef struct mcontext_t
   } mcontext_t;
 
 /* Userlevel context.  */
-typedef struct ucontext_t
+typedef struct ucontext
   {
     unsigned long int  __uc_flags;
-    struct ucontext_t *uc_link;
+    struct ucontext   *uc_link;
     stack_t            uc_stack;
     sigset_t           uc_sigmask;
     /* There's some padding here to allow sigset_t to be expanded in the

libc/sysdeps/linux/tile/sys/ucontext.h

@@ -82,10 +82,10 @@ typedef struct
   } mcontext_t;
 
 /* Userlevel context.  */
-typedef struct ucontext_t
+typedef struct ucontext
   {
     unsigned long int __ctx(uc_flags);
-    struct ucontext_t *uc_link;
+    struct ucontext *uc_link;
     stack_t uc_stack;
     mcontext_t uc_mcontext;
     sigset_t uc_sigmask;