fix sh build regressions in asm

even hidden functions need @PLT symbol references; otherwise an
absolute address is produced instead of a PC-relative one.

src/ldso/sh/dlsym.s

@@ -8,4 +8,4 @@ dlsym:
 1:	 mov.l @r15, r6
 
 .align 2
-L1:	.long __dlsym-(1b-.)
+L1:	.long __dlsym@PLT-(1b-.)

src/thread/sh/syscall_cp.s

@@ -22,7 +22,7 @@ __cp_begin:
 1:
 
 .align 2
-L1:	.long __cancel-(1b-.)
+L1:	.long __cancel@PLT-(1b-.)
 
 2:	mov   r5, r3
 	mov   r6, r4