Clean Up Build Warnings

Make the `FntPrint` function signature consistent between header and
impl and and put guard around duplicate `CLAMP` macro in `libgpu/sys.c`.

Author: hohle

include/psxsdk/libgpu.h

@@ -600,7 +600,7 @@ extern int SetGraphReverse(int mode);
 extern int SetGraphQueue(int mode);
 extern u_long DrawSyncCallback(void (*func)());
 extern void FntLoad(int tx, int ty);
-int FntPrint(const char* fmt, ...);
+long FntPrint(long id, ...);
 extern void SetDispMask(int mask);
 extern void SetDrawMode(DR_MODE* p, int dfe, int dtd, int tpage, RECT* tw);
 extern void SetDumpFnt(int id);

src/main/psxsdk/libgpu/sys.c

@@ -65,8 +65,10 @@ static volatile s32* DPCR = (s32*)0x1F8010F0;
 static volatile s32 _qin = 0;
 static volatile s32 _qout = 0;
 
+#ifndef CLAMP
 #define CLAMP(value, low, high)                                                \
     value < low ? low : (value > high ? high : value)
+#endif
 
 // gpu commands
 #define CMD_CLEAR_CACHE 0x01000000