feat(asm): symbol-valued DATA, division slash in symbols and plain semicolons

Assisted-by: GLM 5.3 Flash

testdata/verify/semicolons_amd64.s

@@ -0,0 +1,21 @@
+#include "textflag.h"
+
+// The kernel exercises the ';' statement separator in a plain file, the way
+// the runtime writes it ("ROLQ $3, DI; ROLQ $13, DI", "REP; MOVSQ").  Each
+// statement assembles exactly as it would on a line of its own.
+
+// func rol(x int64) int64
+TEXT ·rol(SB), NOSPLIT, $0-16
+	ROLQ $3, DI; ROLQ $13, DI
+	MOVQ DI, ret+0(FP)
+	RET
+
+// func move(dst, src unsafe.Pointer)
+TEXT ·move(SB), NOSPLIT, $0-16
+	REP ; MOVSQ
+	RET
+
+TEXT ·paired(SB), NOSPLIT, $0-8
+	XORQ AX, AX; XORQ CX, CX
+	MOVQ AX, ret+0(FP)
+	RET