Implement parser for path section of #include

- This syntax parser can parse 2 forms of #include, including `#include
  "header.h"` (string path form) and `#include <header.h>` (system
  defined path form), the former one is guaranteed to be always parsed,
  however, the later one is not guaranteed will be always successfully
  parsed due to lack of platform support.

src/parser.c

@@ -62,20 +62,6 @@ int get_size(var_t *var, type_t *type)
     return type->size;
 }
 
-/* abort when invalidate is true and the line contains  character other than
- * whitespace */
-void skip_line(int invalidate)
-{
-    /* FIXME: Comments will causes current validation failed. */
-    skip_whitespace();
-    do {
-        if (invalidate && !is_whitespace(peek_char(0)) &&
-            !is_newline(peek_char(0))) {
-            error("Expects whitespace after preprocessor directive");
-        }
-    } while (read_char(0) != '\n');
-}
-
 /* Skips lines where preprocessor match is false, this will stop once next
  * token is either `T_cppd_elif`, `T_cppd_else` or `cppd_endif`.
  */
@@ -114,10 +100,23 @@ int read_preproc_directive()
     char token[MAX_ID_LEN];
 
     if (lex_peek(T_cppd_include, token)) {
-        skip_line(0); /* FIXME: remove this line after syntax parsing is
-                         implemented */
         lex_expect(T_cppd_include);
-        /* TODO: parse include syntax here */
+
+        /* Basic #define syntax validation */
+        if (lex_peek(T_string, NULL)) {
+            /* #define "header.h" */
+            lex_expect(T_string);
+        } else {
+            /* #define <stdlib.h> */
+            lex_expect(T_lt);
+
+            while (!lex_peek(T_gt, NULL)) {
+                next_token = lex_token();
+            }
+
+            lex_expect(T_gt);
+        }
+
         return 1;
     }
     if (lex_accept(T_cppd_define)) {