feat(parser): split plain statements on semicolons in the raw parse

Assisted-by: GLM 5.3 Flash

parser/preproc_test.go

@@ -462,7 +462,9 @@ TEXT ·f(SB), NOSPLIT, $0
 
 func TestParseUnchangedWithoutExpand(t *testing.T) {
 	// Without Expand the preprocessor must not exist: a macro invocation
-	// stays an unexpanded instruction line and ';' keeps the old parse.
+	// stays an unexpanded instruction line.  The ';' statement separator is
+	// not part of the preprocessor: the plain parse path splits on it the
+	// same way the expansion path does, so both spellings agree.
 	f, errs := Parse("t_amd64.s", `
 #define TWICE ADDQ AX, AX
 TEXT ·f(SB), NOSPLIT, $0
@@ -480,7 +482,7 @@ TEXT ·f(SB), NOSPLIT, $0
 			mnemonics = append(mnemonics, in.Mnemonic.Text)
 		}
 	}
-	if strings.Join(mnemonics, " ") != "TWICE BYTE RET" {
+	if strings.Join(mnemonics, " ") != "TWICE BYTE BYTE RET" {
 		t.Errorf("non-expanding parse changed: %v", mnemonics)
 	}
 }