Fix some compilation warnings (Thanks mxf)

src/cfgparse.l

@@ -1,5 +1,6 @@
 %{
 #include <stdio.h>
+#include <string.h>
 #include "cfgparse.tab.h"
 #include <xcb/xcb.h>
 

src/cfgparse.y

@@ -15,6 +15,8 @@
 #include "util.h"
 #include "queue.h"
 #include "table.h"
+#include "workspace.h"
+#include "xcb.h"
 
 extern int yylex(void);
 extern FILE *yyin;

src/config.c

@@ -26,6 +26,10 @@
 #include "table.h"
 #include "workspace.h"
 
+/* prototype for src/cfgparse.y, will be cleaned up as soon as we completely
+ * switched to the new scanner/parser. */
+void parse_file(const char *f);
+
 Config config;
 
 bool config_use_lexer = false;