cgen: fix asm stmt separators (#25067)

vlib/v/gen/c/cgen.v

@@ -3255,7 +3255,7 @@ fn (mut g Gen) asm_stmt(stmt ast.AsmStmt) {
 		}
 
 		if !template.is_label {
-			g.write(';')
+			g.write('\\n\\t')
 		}
 		g.writeln('"')
 	}

vlib/v/slow_tests/assembly/stmt_separator_test.amd64.v

@@ -0,0 +1,48 @@
+import os
+import time
+
+const asm_file_content = '
+fn asm_fn() {
+	mut x := u64(0)
+	mut y := u64(0)
+	mut z := u64(0)
+	mut hi := u64(0)
+	mut lo := u64(0)
+	asm amd64 {
+		mulq rdx
+		addq rax, z
+		adcq rdx, 0
+		; =a (lo)
+		=d (hi)
+		; a (x)
+		  d (y)
+		  r (z)
+		; cc
+	}
+}
+
+fn main() {
+	asm_fn()
+}
+'
+
+const vexe = os.getenv('VEXE')
+const v_file = os.join_path(os.vtmp_dir(), 'generated_stmt_separator.amd64.v')
+const genexe_file = os.join_path(os.vtmp_dir(), 'generated_stmt_separator.exe')
+const c_file = os.join_path(os.vtmp_dir(), 'generated_stmt_separator.exe.tmp.c')
+
+fn test_stmt_separator() {
+	os.write_file(v_file, asm_file_content)!
+	eprintln('Compiling...')
+	compile_cmd := '${os.quoted_path(vexe)} -cg -skip-running -no-rsp -keepc -o ${os.quoted_path(genexe_file)} ${os.quoted_path(v_file)}'
+	eprintln('> compile_cmd: ${compile_cmd}')
+	time.sleep(1000 * time.millisecond) // improve chances of working on windows
+	compile_res := os.system(compile_cmd)
+	assert compile_res == 0
+
+	content := os.read_file(c_file)!
+	os.rm(v_file)!
+	os.rm(genexe_file)!
+	os.rm(c_file)!
+	assert content.contains(r'addq %[z], %%rax\n\t')
+}