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12.19 Single Suffix Rules and Separated Dependencies
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A “Single Suffix Rule” is basically a usual suffix (inference) rule
(‘.from.to:’), but which _destination_ suffix is empty (‘.from:’).

   “Separated dependencies” simply refers to listing the prerequisite of
a target, without defining a rule.  Usually one can list on the one hand
side, the rules, and on the other hand side, the dependencies.

   Solaris ‘make’ does not support separated dependencies for targets
defined by single suffix rules:

     $ cat Makefile
     .SUFFIXES: .in
     foo: foo.in
     .in:
             cp $< $@
     $ touch foo.in
     $ make
     $ ls
     Makefile  foo.in

while GNU Make does:

     $ gmake
     cp foo.in foo
     $ ls
     Makefile  foo       foo.in

   Note it works without the ‘foo: foo.in’ dependency.

     $ cat Makefile
     .SUFFIXES: .in
     .in:
             cp $< $@
     $ make foo
     cp foo.in foo

and it works with double suffix inference rules:

     $ cat Makefile
     foo.out: foo.in
     .SUFFIXES: .in .out
     .in.out:
             cp $< $@
     $ make
     cp foo.in foo.out

   As a result, in such a case, you have to write target rules.