build: add opencv5 to the list of pkgconfig names

[de-vri-es]

On Arch Linux, the pkgconfig file for opencv5 is called "opencv5.pc". This seems like a vanilla upstream filename.

See https://archlinux.org/packages/extra/x86_64/opencv/ for the package details.

[twistedfall]

Thanks a lot!

[AlexanderStein]

Unfortunately with this, a opencv5 installation hides a parallel opencv4 installation breaking at compile time:

error[E0433]: cannot find `features` in `crate`
    --> /tmp/test/target/debug/build/opencv-7f20f0ffea32c899/out/opencv/objdetect.rs:1221:166
     |
1221 |     pub fn find_circles_grid(image: &impl ToInputArray, pattern_size: core::Size, centers: &mut impl ToOutputArray, flags: i32, blob_detector: Option<&core::Ptr<crate::features::Feature2D>>) -> Result<bool> {
     |                                                                                                                                                                         ^^^^^^^^ could not find `features` in the crate root

error[E0433]: cannot find `features` in `crate`
    --> /tmp/test/target/debug/build/opencv-7f20f0ffea32c899/out/opencv/objdetect.rs:1270:178
     |
1270 | ...enters: &mut impl ToOutputArray, flags: i32, blob_detector: Option<&core::Ptr<crate::features::Feature2D>>, parameters: crate::objdetect::CirclesGridFinderParameters) -> Result<bool> {
     |                                                                                         ^^^^^^^^ could not find `features` in the crate root

error[E0433]: cannot find `dnn` in `crate`
    --> /tmp/test/target/debug/build/opencv-7f20f0ffea32c899/out/opencv/objdetect.rs:6123:37
     |
6123 |         pub fn create_1(net: &impl crate::dnn::NetTraitConst) -> Result<core::Ptr<crate::objdetect::CCheckerDetector>> {
     |

In other words I have both opencv5 and opencv4 (via AUR) installed, but my project requires opencv4, but opencv5 is selected

[de-vri-es]

You can still set OPENCV_PACKAGE_NAME to force opencv4 to be selected. It seems sensible to me that 5 is selected by default in this scenario.

[AlexanderStein]

You can still set OPENCV_PACKAGE_NAME to force opencv4 to be selected. It seems sensible to me that 5 is selected by default in this scenario.

Ah nice. Thanks. There is also OPENCV_PKGCONFIG_NAME which seems more appropriate in my case. But this does the trick. So yeah opencv5 can be the default if it is overwritable.