Automake supports a simple type of conditionals.
These conditionals are not the same as conditionals in
GNU Make. Automake conditionals are checked at configure time by the
configure script, and affect the translation from
Makefile.in to Makefile. They are based on options passed
to configure and on results that configure has discovered
about the host system. GNU Make conditionals are checked at
time, and are based on variables passed to the make program or defined
in the Makefile.
Automake conditionals will work with any make program.