[dev.cc] runtime: convert assembly files for C to Go transition

The main change is that #include "zasm_GOOS_GOARCH.h"
is now #include "go_asm.h" and/or #include "go_tls.h".

Also, because C StackGuard is now Go _StackGuard,
the assembly name changes from const_StackGuard to
const__StackGuard.

In asm_$GOARCH.s, add new function getg, formerly
implemented in C.

The renamed atomics now have Go wrappers, to get
escape analysis annotations right. Those wrappers
are in CL 174860043.

LGTM=r, aram
R=r, aram
CC=austin, dvyukov, golang-codereviews, iant, khr
https://golang.org/cl/168510043
diff --git a/src/runtime/sys_netbsd_arm.s b/src/runtime/sys_netbsd_arm.s
index 039a083..fa9bc57 100644
--- a/src/runtime/sys_netbsd_arm.s
+++ b/src/runtime/sys_netbsd_arm.s
@@ -6,7 +6,8 @@
 // /usr/src/sys/kern/syscalls.master for syscall numbers.
 //
 
-#include "zasm_GOOS_GOARCH.h"
+#include "go_asm.h"
+#include "go_tls.h"
 #include "textflag.h"
 
 // Exit the entire program (like C exit)
@@ -330,7 +331,7 @@
 	SWI $0xa0005c	// sys_fcntl
 	RET
 
-TEXT runtime·casp(SB),NOSPLIT,$0
+TEXT runtime·casp1(SB),NOSPLIT,$0
 	B	runtime·cas(SB)
 
 // TODO(minux): this is only valid for ARMv6+