fix(asm): place the arm64 literal pool the way the toolchain flushes it

Assisted-by: GLM 5.3

asm/arm64_frame.go

@@ -495,6 +495,10 @@ func arm64GuardBytes(fi arm64FrameInfo, blockStart int) []byte {
 	return a64WordsLE(ws...)
 }
 
+// arm64MoreStackBlockLen is the byte length of arm64MoreStackBlock: the
+// saved LR, the BL and the branch back, three words whatever the target.
+const arm64MoreStackBlockLen = 12
+
 // arm64MoreStackBlock emits the trailing block: MOVD R30, R3 (save LR),
 // BL runtime.morestack_noctxt, B back to the function start.  The BL carries
 // the R_CALLARM64 relocation.