tests: Fix Makefile.test to not allow host includes

xics was including the host limits.h for example

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

tests/Makefile.test

@@ -9,7 +9,7 @@ CC = $(CROSS_COMPILE)gcc
 LD = $(CROSS_COMPILE)ld
 OBJCOPY = $(CROSS_COMPILE)objcopy
 
-CFLAGS = -Os -g -Wall -std=c99 -msoft-float -mno-string -mno-multiple -mno-vsx -mno-altivec -mlittle-endian -fno-stack-protector -mstrict-align -ffreestanding -fdata-sections -ffunction-sections -I ../../include
+CFLAGS = -Os -g -Wall -std=c99 -nostdinc -msoft-float -mno-string -mno-multiple -mno-vsx -mno-altivec -mlittle-endian -fno-stack-protector -mstrict-align -ffreestanding -fdata-sections -ffunction-sections -I ../../include -isystem $(shell $(CC) -print-file-name=include)
 ASFLAGS = $(CFLAGS)
 LDFLAGS = -T powerpc.lds
 

tests/xics/xics.c

@@ -1,7 +1,6 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <stdbool.h>
-#include <limits.h>
 
 #include "console.h"
 #include "xics.h"