Assuming we have the rule:
a: b c d e
and b, c, d and e are independent of each other.
Is the order of making b, c, d, e defined? It seems that generally they will be made in order b, c, d, e, but may it sometimes happen, that the order will be different?
I'll just add this for future reference. While GNU Make may not define a specific order when it comes to processing prerequisites, POSIX make requires that they be handled in the order they've been specified, namely left-to-right. Most implementations follow this rule. POSIX even gives an example where a make implementation not following this rule could break the build process of a program:
foo: y.tab.o lex.o main.o
$(CC) $(CFLAGS) -o $@ t.tab.o lex.o main.o
where lex.o ends up using an incorrect y.tab.h. While this can be rewritten in a way that works with GNU Make, I thought I'd share this tidbit about prerequisite ordering.
If order matters, you can selectively enforce it using recursive make. For example, suppose you don't care what order b and c are made in, as long as they're both made before d and d is made before e. Then you could write your rule as:
a: b c
$(MAKE) d
$(MAKE) e
# Additional steps to make a
Be aware that depending on the complexity of d and e, this approach may do Bad Things to your build times: see Recursive Make Considered Harmful (PDF) for arguments against doing it this way.