cleanup use of visibility attributes in pthread_cancel.c

applying the attribute to a weak_alias macro was a hack. instead use a
separate declaration to apply the visibility, and consolidate
declarations together to avoid having visibility mess all over the
file.

src/thread/pthread_cancel.c

@@ -4,12 +4,11 @@
 #include "libc.h"
 
 #ifdef SHARED
-#define hidden __attribute__((__visibility__("hidden")))
-#else
-#define hidden
+__attribute__((__visibility__("hidden")))
 #endif
+long __cancel(), __cp_cancel(), __syscall_cp_asm(), __syscall_cp_c();
 
-hidden long __cancel()
+long __cancel()
 {
 	pthread_t self = __pthread_self();
 	if (self->canceldisable == PTHREAD_CANCEL_ENABLE || self->cancelasync)
@@ -22,14 +21,12 @@ hidden long __cancel()
  * definition of __cp_cancel to undo those adjustments and call __cancel.
  * Otherwise, __cancel provides a definition for __cp_cancel. */
 
-hidden weak_alias(__cancel, __cp_cancel);
+weak_alias(__cancel, __cp_cancel);
 
-hidden
 long __syscall_cp_asm(volatile void *, syscall_arg_t,
                       syscall_arg_t, syscall_arg_t, syscall_arg_t,
                       syscall_arg_t, syscall_arg_t, syscall_arg_t);
 
-hidden
 long __syscall_cp_c(syscall_arg_t nr,
                     syscall_arg_t u, syscall_arg_t v, syscall_arg_t w,
                     syscall_arg_t x, syscall_arg_t y, syscall_arg_t z)
@@ -55,12 +52,16 @@ static void _sigaddset(sigset_t *set, int sig)
 	set->__bits[s/8/sizeof *set->__bits] |= 1UL<<(s&8*sizeof *set->__bits-1);
 }
 
+#ifdef SHARED
+__attribute__((__visibility__("hidden")))
+#endif
+extern const char __cp_begin[1], __cp_end[1];
+
 static void cancel_handler(int sig, siginfo_t *si, void *ctx)
 {
 	pthread_t self = __pthread_self();
 	ucontext_t *uc = ctx;
 	const char *ip = ((char **)&uc->uc_mcontext)[CANCEL_REG_IP];
-	hidden extern const char __cp_begin[1], __cp_end[1];
 
 	a_barrier();
 	if (!self->cancel || self->canceldisable == PTHREAD_CANCEL_DISABLE) return;