Order-only prerequisites without assuming GNU make

[Reuben Thomas]

Hi,

I need an order-only prerequisite, but I don't want to assume GNU make. What 
should I do?

In case it helps, the exact problem I have is this: I'm using help2man in my 
project. Users have complained that it's not widely installed, and can be 
tricky to install on older systems (because of its Perl dependencies). 
Hence, I want to make it necessary only for maintainers.

In fact, the man page is already distributed built, but it's always rebuilt, 
because as it's generated by help2man, it depends on the executable. 
However, it *really* should depend on just my main.c source file (which 
contains the help message).

But, if I make it depend on the source file, then make can fail, because it 
can try to build the man page before the executable. So I need an order-only 
prerequisite of the executable...

The obvious way around this is the (somewhat annoying) one of putting the 
man page in a separate directory, and using SUBDIRS in the top-level 
Makefile.am to get the ordering I want, but is there anything less drastic I 
can do?

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