tests: Take in account Makefiles that have meaning for rebuild only.
Currently, targets dependancy list don't include Makefile.in,
this leads to incomplete rebuild after target's compiler/linker
flags was changed.
Use "$(wildcard)" function due to Makefile.in could be absent
in subdirectory.
Signed-off-by: Leonid Lisovskiy <lly.dev@gmail.com>