Add function marks and size indications

Add a macro to annotate function end and start using both ENTRY and END
for each function. This allows valgrind (and presumably other debugging
tools) to use the debug symbols to trace the functions.

Change-Id: I5f09cef8e22fb356eb6f5cee952b031e567599b6
diff --git a/libc/arch-arm/bionic/tkill.S b/libc/arch-arm/bionic/tkill.S
index 7b3301a..fdc5ed4 100644
--- a/libc/arch-arm/bionic/tkill.S
+++ b/libc/arch-arm/bionic/tkill.S
@@ -32,18 +32,15 @@
    abort due to a fatal runtime error (e.g. detection
    of a corrupted malloc heap).
 */
+
 #include <sys/linux-syscalls.h>
+#include <machine/asm.h>
 
 #ifndef __NR_tkill
 #define __NR_tkill  238
 #endif
 
-    .text
-    .type tkill, #function
-    .globl tkill
-    .align 4
-
-tkill:
+ENTRY(tkill)
     stmfd   sp!, {r4-r7, ip, lr}
     ldr     r7, =__NR_tkill
     swi     #0
@@ -51,3 +48,4 @@
     movs    r0, r0
     bxpl    lr
     b       __set_syscall_errno
+END(tkill)