Make the lexer reentrant (to avoid "still reachable" memory).

This allows the final program to be 100% "valgrind clean", (freeing
all memory that it allocates). This will make it much easier to ensure
that any allocation that parser actions perform are also cleaned up.

glcpp-lex.l

@@ -28,7 +28,7 @@
 #include "glcpp-parse.h"
 %}
 
-%option noyywrap
+%option reentrant noyywrap
 
 %%
 

glcpp-parse.y

@@ -28,10 +28,13 @@
 #define YYSTYPE int
 
 void
-yyerror (const char *error);
+yyerror (const char *error, void *scanner);
 
 %}
 
+%parse-param {void *scanner}
+%lex-param {void *scanner}
+
 %token TOKEN
 
 %%
@@ -51,7 +54,7 @@ token:		TOKEN
 %%
 
 void
-yyerror (const char *error)
+yyerror (const char *error, void *scanner)
 {
 	fprintf (stderr, "Parse error: %s\n", error);
 }

glcpp.c

@@ -24,5 +24,12 @@
 int
 main (void)
 {
-	return yyparse ();
+	int ret;
+	void *scanner;
+
+	yylex_init (&scanner);
+	ret = yyparse (scanner);
+	yylex_destroy (scanner);
+
+	return ret;
 }