bug#49122: gobject-introspection and not finding cairo

[Raghav Gururajan via Bug reports for GNU Guix]

Hi John!

Something like this:

```
(define-public gobject-introspection+cairo
   (hidden-package
    (package
      (inherit gobject-introspection)
      (arguments

         ((#:configure-flags flags ''())
          `(cons* "-Dcairo=true" ,flags))))
      (inputs
       `(("cairo" ,cairo)
         ,@(package-inputs gobject-introspection))))))
```

      (substitute-keyword-arguments (package-arguments gobject-introspection)

Or, something like this:

```
(define-public gobject-introspection+cairo
  (hidden-package
   (package
     (inherit gobject-introspection)
     (arguments

        ((#:configure-flags flags ''())
         `(append
           (list
            "-Dcairo=true"
            (string-append "-Dcairo_libname="
                           (assoc-ref %build-inputs "cairo")
                           "/lib/libcairo-gobject.so"))
           ,flags))))
     (inputs
      `(("cairo" ,cairo)
        ,@(package-inputs gobject-introspection))))))
```

Regards,
RG.

(substitute-keyword-arguments (package-arguments gobject-introspection)

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