Building Qt against specific OpenGL library

[Mamegohan]

EDIT 2 : Editing qtbase/mkspecs/common/linux.conf and entering:
QMAKE_INCDIR_OPENGL = /usr/local/include
QMAKE_LIBDIR_OPENGL = /usr/local/lib
didn't seem to work - Qt still links against /usr/lib/x86_64-linux-gnu/mesa/libGL.so.1, not /usr/local/lib/libGL.so as I would like. So I'm still open to suggestions.

EDIT: Ah, I think I get it - I need to edit the mkspec. Will mark this as solved once I can confirm that it worked.

I'm using Qt 5.5 on Linux Mint. I want to use a more recent version of Mesa than the one installed with the system, since I want support for version 3.30 of GLSL. Therefore I've compiled my own Mesa and installed it in /usr/local/.

Questions:

1. I assume that I have to link my application against a version of Qt that is compiled against the new Mesa lib - I can't just link my application to the new OpenGL lib. Is this correct?

2. If so, how can I tell Qt to compile itself against a specific OpenGL lib? I've already successfully compiled Qt 5.5 from git, but it's linked against the "system" opengl lib.

Thanks in advance!