[Patch] add pkg-config file support

[Yoran Heling]

(I accidentally sent the below message directly to Dennis rather than to
the list, so I'm sending it again for others to read. Sorry, Dennis, for
the repeated message.)

Hi,

I'll voice my opinion on this as a user of libev and as someone who
loves having his software work out of the box on all Linux distros.

On 2013-03-07, Dennis Lan (dlan) wrote:
> Hi Marc：                                                                                                                                                                                                                                                                      
>    It's quite obvious.                                                                                                                                                                                                                                                         
>    With this patch, Any package depend on libev can use pkg-config to                                                                                                                                                                                                          
> detect/check.                                                                                                                                                                                                                                                                  
> Retrieve the cflags, libs, or other information (make life easier).                                                                                                                                                                                                            
>    Yes, it's a quite trivial patch, but useful. And It doesn't hurts?                                                                                                                                                                                                          

It does hurt. Now an applications needs *TWO* checks. One to see if
pkg-config is installed and whether it has something to say about libev,
and another fallback mechanism to the classic mode of checking whether
ev.h and -lev work.

(Okay, arguably, there isn't even a need for any checking at all. One
could just include ev.h and link against -lev normally. Having a
configure script check whether something like that will succeed does
happen to be customary, and catches any possible errors earlier in the
building process)

I don't particularly mind pkg-config in general, but if it's going to be
used, it only makes sense that *all* distros recognize the package and
that it works for *all* versions of the library that the application can
use. Adding pkg-config support at this point won't help at all.

Just my two cents,

Yoran.