Make -E to imply -xc

main.c

@@ -203,6 +203,10 @@ static void parse_args(int argc, char **argv) {
 
   if (input_paths.len == 0)
     error("no input files");
+
+  // -E implies that the input is the C macro language.
+  if (opt_E)
+    opt_x = FILE_C;
 }
 
 static FILE *open_file(char *path) {

test/driver.sh

@@ -198,4 +198,8 @@ echo 'int x;' > $tmp/foo.c
 $chibicc -c -x assembler -x none -o $tmp/foo.o $tmp/foo.c
 check '-x none'
 
+# -E
+echo foo | $chibicc -E - | grep -q foo
+check -E
+
 echo OK