In addition to target-specific variable values (see Target-specific Variable Values), GNU make supports
pattern-specific variable values. In this form, a variable is defined
for any target that matches the pattern specified. Variables defined in
this way are searched after any target-specific variables defined
explicitly for that target, and before target-specific variables defined
for the parent target.
Set a pattern-specific variable value like this:
pattern ... : variable-assignment
or like this:
pattern ... : override variable-assignment
where pattern is a %-pattern. As with target-specific variable
values, multiple pattern values create a pattern-specific variable
value for each pattern individually. The variable-assignment can
be any valid form of assignment. Any command-line variable setting will
take precedence, unless override is specified.
For example:
%.o : CFLAGS = -O
will assign CFLAGS the value of -O for all targets
matching the pattern %.o.