riscv: Fix incorrect jal with HIDDEN_JUMPTARGET

A non-local STV_DEFAULT defined symbol is by default preemptible in a
shared object. j/jal cannot target a preemptible symbol. On other
architectures, such a jump instruction either causes PLT [BZ #18822], or
if short-ranged, sometimes rejected by the linker (but not by GNU ld's
riscv port [ld PR/28509]).

Use HIDDEN_JUMPTARGET to target a non-preemptible symbol instead.

With this patch, ld.so and libc.so can be linked with LLD if source
files are compiled/assembled with -mno-relax/-Wa,-mno-relax.

Acked-by: Palmer Dabbelt <palmer@dabbelt.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/riscv/setjmp.S

@@ -21,7 +21,7 @@
 
 ENTRY (_setjmp)
   li	a1, 0
-  j	__sigsetjmp
+  j	HIDDEN_JUMPTARGET (__sigsetjmp)
 END (_setjmp)
 ENTRY (setjmp)
   li	a1, 1

sysdeps/unix/sysv/linux/riscv/setcontext.S

@@ -95,6 +95,7 @@ LEAF (__setcontext)
 99:	j	__syscall_error
 
 END (__setcontext)
+libc_hidden_def (__setcontext)
 weak_alias (__setcontext, setcontext)
 
 LEAF (__start_context)
@@ -108,7 +109,7 @@ LEAF (__start_context)
 	/* Invoke subsequent context if present, else exit(0).  */
 	mv	a0, s2
 	beqz	s2, 1f
-	jal	__setcontext
-1:	j	exit
+	jal	HIDDEN_JUMPTARGET (__setcontext)
+1:	j	HIDDEN_JUMPTARGET (exit)
 
 END (__start_context)