how to code if/then/else in makefile

[Robert P. J. Day]

  a colleague is writing a makefile that will test a setting for an
architecture variable that might have a number of different values, so
he obviously wants some kind of if/then/else based on simple string
comparison.  one of these possibilities will the an unset variable
(empty string) identifying a native build.

  oddly, he told me that he can't do a string compare against an empty
string and had to resort to "ifndef".  what's the standard way to
implement what's equivalent to a case structure based on string
compares, with an "else" equivalent at the bottom?  thanks.

rday