As of automake-13.1 the INCLUDES directive is no longer supported.
An automake run will return with an error.
This changeset simply follows automake's advice to replace INCLUDES
by AM_CPPFLAGS.
$< isn't supported in BSD make say. $(RM) is pre-defined in GNU make
though, not in BSD make say. so changed to check on configure if it's
pre-defined by make, otherwise set the appropriate command to $(RM).
This would be a workaround until it has the certain pre-defined value.
Sebastian Freundt
Behdad Esfahbod
Akira TAGOH