all: mark the trampoline symbol hidden

this should not be a part of the public ABI

arch/common/common-trampoline.c

@@ -14,6 +14,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 
+__attribute__ ((visibility ("hidden")))
 void
 libucontext_trampoline(void)
 {

arch/mips/startcontext.S

@@ -14,6 +14,7 @@ LOCALSZ = 1
 
 #include "defs.h"
 
+.hidden libucontext_trampoline
 FUNC(libucontext_trampoline)
 	move	$gp, $s1
 

arch/mips64/startcontext.S

@@ -14,6 +14,7 @@ LOCALSZ = 1
 
 #include "defs.h"
 
+.hidden libucontext_trampoline
 FUNC(libucontext_trampoline)
 	move	$gp, $s1
 

arch/s390x/startcontext.S

@@ -12,6 +12,7 @@
 
 #include "defs.h"
 
+.hidden libucontext_trampoline
 FUNC(libucontext_trampoline)
 	basr	%r14, %r7			/* run function pointer (%r7) and return here */
 	ltgr	%r8, %r8			/* check to see if uc_link (%r8) is null */