rename dynamic linker entry point from _start to _dlstart

the main motivation for this change is to aid in debugging. since the
main program's entry point is also named _start, it was difficult to
set breakpoints or quickly identify which _start execution stopped in.

Makefile

@@ -125,7 +125,7 @@ $(foreach s,$(wildcard src/*/$(ARCH)*/*.s),$(eval $(call mkasmdep,$(s))))
 
 lib/libc.so: $(LOBJS)
 	$(CC) $(CFLAGS_ALL_SHARED) $(LDFLAGS) -nostdlib -shared \
-	-Wl,-e,_start -Wl,-Bsymbolic-functions \
+	-Wl,-e,_dlstart -Wl,-Bsymbolic-functions \
 	-o $@ $(LOBJS) $(LIBCC)
 
 lib/libc.a: $(OBJS)

src/ldso/arm/start.s

 .text
-.global _start
-_start:
+.global _dlstart
+_dlstart:
 	ldr r0,[sp]
 	add r1,sp,#4
 	bl __dynlink

src/ldso/i386/start.s

 .text
-.global _start
-_start:
+.global _dlstart
+_dlstart:
 	xor %ebp,%ebp
 	pop %edi
 	mov %esp,%esi

src/ldso/microblaze/start.s

 # FIXME: clearing argv entries
-.global _start
-_start:
+.global _dlstart
+_dlstart:
 	add     r19, r0, r0
 
 	lw      r5, r0, r1

src/ldso/mips/start.s

@@ -2,9 +2,9 @@
 .hidden __reloc_self
 .set noreorder
 .set nomacro
-.global _start
-.type _start,@function
-_start:
+.global _dlstart
+.type _dlstart,@function
+_dlstart:
 	move $fp, $0
 
 	bgezal $0, 1f

src/ldso/powerpc/start.s

-	.global _start
-	.type   _start,@function
-_start:
+	.global _dlstart
+	.type   _dlstart,@function
+_dlstart:
 	bl      1f
 2:	.long   _DYNAMIC-2b
 1:	mflr    5

src/ldso/sh/start.s

 .text
-.global _start
-.type   _start, @function
-_start:
+.global _dlstart
+.type   _dlstart, @function
+_dlstart:
 	mov.l  @r15, r4
 	mov    r15, r5
 	mov.l  L1, r0

src/ldso/x32/start.s

 .text
-.global _start
-_start:
+.global _dlstart
+_dlstart:
 	mov (%rsp),%rdi  /* move argc into 1st argument slot */
 	lea 4(%rsp),%rsi /* move argv into 2nd argument slot */
 	call __dynlink

src/ldso/x86_64/start.s

 .text
-.global _start
-_start:
+.global _dlstart
+_dlstart:
 	mov (%rsp),%rdi
 	lea 8(%rsp),%rsi
 	call __dynlink