-I. Note the dot to show the current directory. Ignore the protmode error or remove the line from the DEF file. The other errors might be fixed by the -I. more likely there is a missing library or macro.
Hmm, seems that min and max macros are defined in the toolkits stdlib.h but not in the kLIBC stdlib.h. Not sure about the best way to use the toolkits stdlib.h so simplest to add the macro.
Add
#define max(a,b) (((a) > (b)) ? (a) : (b))
#define min(a,b) (((a) < (b)) ? (a) : (b))
to sysvals.c, at about line 14, so you have
#include <stdlib.h>
#include <string.h>
#include "sysvals.h"
#define max(a,b) (((a) > (b)) ? (a) : (b))
#define min(a,b) (((a) < (b)) ? (a) : (b))
MRESULT EXPENTRY ClientWndProc (HWND, ULONG, MPARAM, MPARAM) ;
LONG RtJustCharStringAt (HPS, PPOINTL, LONG, PCHAR) ;
and test.