[dev.regabi] runtime: don't mark rt0_go ABIInternal

rt0_go is not actually ABIInternal, and it actually has callers
(e.g. _rt0_amd64).

Change-Id: Id730176e620ad9f443e6bfca6ded81a1367531ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/289193
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

src/runtime/asm_amd64.s

@@ -84,9 +84,7 @@ GLOBL _rt0_amd64_lib_argc<>(SB),NOPTR, $8
 DATA _rt0_amd64_lib_argv<>(SB)/8, $0
 GLOBL _rt0_amd64_lib_argv<>(SB),NOPTR, $8
 
-// Defined as ABIInternal since it does not use the stack-based Go ABI (and
-// in addition there are no calls to this entry point from Go code).
-TEXT runtime·rt0_go<ABIInternal>(SB),NOSPLIT,$0
+TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	// copy arguments forward on an even stack
 	MOVQ	DI, AX		// argc
 	MOVQ	SI, BX		// argv