It's really a bug in flex that these functions are generated with neither
a declaration nor the 'static' keyword, but we can at least avoid the
warnings this way.
#include "glcpp.h"
#include "glcpp-parse.h"
+/* Flex annoyingly generates some functions without making them
+ * static. Let's declare them here. */
+int glcpp_get_column (yyscan_t yyscanner);
+void glcpp_set_column (int column_no , yyscan_t yyscanner);
+
#define YY_USER_ACTION \
do { \
yylloc->source = 0; \