6.12 Pattern-specific Variable Values
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In addition to target-specific variable values (*note Target-specific
Variable Values: Target-specific.), GNU `make' supports
pattern-specific variable values.  In this form, the variable is
defined for any target that matches the pattern specified.

   Set a pattern-specific variable value like this:

     PATTERN ... : 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'.

   If a target matches more than one pattern, the matching
pattern-specific variables with longer stems are interpreted first.
This results in more specific variables taking precedence over the more
generic ones, for example:

     %.o: %.c
             $(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

     lib/%.o: CFLAGS := -fPIC -g
     %.o: CFLAGS := -g

     all: foo.o lib/bar.o

   In this example the first definition of the `CFLAGS' variable will
be used to update `lib/bar.o' even though the second one also applies
to this target. Pattern-specific variables which result in the same
stem length are considered in the order in which they were defined in
the makefile.

   Pattern-specific variables are searched after any target-specific
variables defined explicitly for that target, and before target-specific
variables defined for the parent target.