H8: Honor USER_LABEL_PREFIX set by ld

This patch complements the following binutils patch: https://sourceware.org/pipermail/binutils/2026-August/150974.html.

Signed-off-by: Jan Dubiec <jdx@o2.pl>

newlib/libc/sys/h8300hms/crt0.S

@@ -11,8 +11,8 @@
 #ifdef __H8300__
 
 	.section .text
-	.global	_start
-_start:
+	.global	__start
+__start:
 	mov.w	#_stack,sp
 	mov.w	#_edata,r0
 	mov.w	#_end,r2
@@ -43,8 +43,8 @@ _stack:	.space	2
 #if defined (__H8300H__) || defined (__H8300S__) || defined (__H8300SX__)
 
 	.section .text
-	.global	_start
-_start:
+	.global	__start
+__start:
 #ifdef __NORMAL_MODE__
 	mov.w	#_stack,sp
 	mov.w	#_edata,r0