Use tag_c.h as first include in build with C compiler (#1273)

This will fail on MinGW because its gcc does not have wchar_t without
including wchar.h. With g++ as used with test_tag_c.cpp, the problem is
undetected because g++ supports wchar_t without including wchar.h.

examples/tagreader_c.c

@@ -22,11 +22,11 @@
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include "tag_c.h"
+
 #include <stdio.h>
 #include <string.h>
 
-#include "tag_c.h"
-
 #ifndef FALSE
 #define FALSE 0
 #endif