Use #include "foo.h" for including Windows headers in dlls/, use
#include <bar.h> for including Windows headers in include/.

diff --git a/include/odbcinst.h b/include/odbcinst.h
index bee34cf..569a0ed 100644
--- a/include/odbcinst.h
+++ b/include/odbcinst.h
@@ -23,7 +23,7 @@
 extern "C" {
 #endif
 
-#include "sql.h"
+#include <sql.h>
 
 /* flags for Installer function requests */
 #define ODBC_INSTALL_INQUIRY 	1