must not use pkg-config to find EGL on Raspberry Pi

Hi,

it's been some days I'm working on it.
I'm trying to compile meta-qt5 for Yocto with the RaspberryPi.

To summarize:
RaspberryPi can link with: -lEGL -lGLESv2 and can't with -lGLESv2 -lEGL

I was looking on RaspberryPi side first and found out that they properly feed pkg-config.
Then I went into meta-qt5 and found out that... other BSP layers adds some weird patches to have EGL working.
I did not want any patch and kept digging.

When you use pkg-config, you feed "libs" variable and in the ./config.tests/qpa/egl/egl.pro file, you are looking for QMAKE_LIBS_EGL.

So... you set libs and take the default of QMAKE_LIBS_EGL.
With the RaspberryPi, libs = -lEGL -lGLESv2 ... and the default is QMAKE_LIBS_EGL = -lEGL.

=> -lEGL -lGLESv2 -lEGL => -lGLESv2 -lEGL => can't link

I think that you want to keep the pkg-config functionnality AND the QMAKE_LIBS_EGL variable... Which is set to the default value!!!

What should be done is:
If pkg-config then don't take QMAKE_LIBS_EGL into account unless QMAKE_LIBS_EGL is also properly set.

I guess that was what the guy who wrote this configure part thought. But the variable QMAKE_LIBS_EGL computed in the configure does not pass to the egl.pro file.

I'll paste extracts. And hope we will correct it together.