Require GNU make to build binutils-gdb

[Simon Marchi]

On 2016-11-17 15:42, Paul Smith wrote:
> Regarding the patch linked to earlier, I wonder why multiple pattern
> rules were added, rather than just using VPATH plus a few pattern rules
> / explicit rules for the special cases?
> 
> I didn't check carefully.

Are you talking about gdb/Makefile.in?  Could you be more specific?  I 
am not a Makefile expert, so if there's a better way to do what I did, 
I'd like to learn about it.

> If you want to check for 3.81, you could look for the .FEATURES 
> variable
> instead of .VARIABLES; .FEATURES was introduced in 3.81 and is intended
> to let your makefile query what features are available without worrying
> about specific versions.
> 
> It's also never empty, if it exists.  It has one nice advantage in that
> it's a static value, while .VARIABLES requires GNU make to create a 
> list
> of the names of all the variables.  But, if this check is done early
> that's not such a big deal.
> 
> 3.81 was released 10.5 years ago (Apr 2006).

Thanks for the tip.  I found the original gcc patch that added the 3.80 
checking code, it also mentions .FEATURES for checking for 3.81:

   https://gcc.gnu.org/ml/gcc-patches/2008-04/msg01018.html

> automake, technically, generates POSIX compliant makefiles that don't
> rely on GNU make features at all and should work with a wide range of
> different make implementations.
> 
> At least, that's how it is unless something has changed since I looked
> last.

I think you're right. Skimming the automake manual, I saw some mentions 
of tricks you could use if you assumed GNU make would be used.  So in 
the best case, requiring GNU make unlocks some features we could not 
have used otherwise, and worst case it doesn't change anything.