Ensure internal header files are used from mk1mf based builds

Reviewed-by: Richard Levitte: <levitte@openssl.org>

util/mk1mf.pl

diff --git a/util/mk1mf.pl b/util/mk1mf.pl
index 08e0d3c..e3d6c30 100755
--- a/util/mk1mf.pl
+++ b/util/mk1mf.pl
@@ -729,7 +729,7 @@
 # Don't touch anything below this point
 ######################################################
 
-INC=-I\$(INC_D) -I\$(INCL_D)
+INC=-I\$(INC_D) -I\$(INCL_D) -I\$(SRC_D)${o}crypto${o}include
 APP_CFLAGS=\$(INC) \$(CFLAG) \$(APP_CFLAG)
 LIB_CFLAGS=\$(INC) \$(CFLAG) \$(LIB_CFLAG)
 SHLIB_CFLAGS=\$(INC) \$(CFLAG) \$(LIB_CFLAG) \$(SHLIB_CFLAG)