B_FIND_PATH_DEVELOP_HEADERS_DIRECTORY : bad expansion

[Sylvain78]

B_FIND_PATH_DEVELOP_HEADERS_DIRECTORY expands to /system/boot/system/... in the Makefile.
platform is Haiku hrev55344 x86_64

[adamfowleruk]

Thanks! Added to user requested so we can look at this soon. Not sure who will get to it first though, so not assigning myself right now.