fix cstest Makefile

[imbillow]

fix

cc src/*.c -Iinclude -o build/cstest -lcmocka -lcapstone -L../..
In file included from src/arm64_detail.c:5:
include/factory.h:8:10: fatal error: capstone/capstone.h: No such file or directory
    8 | #include <capstone/capstone.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.
In file included from src/arm_detail.c:5:
include/factory.h:8:10: fatal error: capstone/capstone.h: No such file or directory
    8 | #include <capstone/capstone.h>
      |          ^~~~~~~~~~~~~~~~~~~~~
compilation terminated.

[kabeor]

Cool, thx!