Don't use an anonymous label in arm's __bionic_clone.

All the other architectures name this label. Copy them.

(Following discussion of d30bc9e74b8ff3afceac973d334023564e64dbd2.)

Bug: https://llvm.org/bugs/show_bug.cgi?id=30308
Change-Id: I4f20163f569041180d87c79ce6ed856b70704271
diff --git a/libc/arch-arm/bionic/__bionic_clone.S b/libc/arch-arm/bionic/__bionic_clone.S
index a85ea34..8836748 100644
--- a/libc/arch-arm/bionic/__bionic_clone.S
+++ b/libc/arch-arm/bionic/__bionic_clone.S
@@ -51,7 +51,7 @@
 
     # Are we the child?
     movs    r0, r0
-    beq     1f
+    beq     .L_bc_child
 
     # In the parent, reload saved registers then either return or set errno.
     ldmfd   sp!, {r4, r5, r6, r7}
@@ -60,9 +60,9 @@
     neg     r0, r0
     b       __set_errno_internal
 
-    # The child.
-    # Setting lr to 0 will make the unwinder stop at __start_thread
-1:  mov    lr, #0
+.L_bc_child:
+    # Setting lr to 0 will make the unwinder stop at __start_thread.
+    mov    lr, #0
     # Call __start_thread with the 'fn' and 'arg' we stored on the child stack.
     pop    {r0, r1}
     b      __start_thread