New: glmark2 - OpenGL benchmark

Hi,

Attached is a new port of glmark2. This is an OpenGL benchmark. In its
default configuration, it runs a series of scenes and ends in a score
that can be used to compare performance of 3D-accelerated graphics
between different machines, or also with the performance on other
platforms (Linux...). At this point, it builds only with x11-* flavors,
not drm-* (which needs udev).

I built it and ran on my Intel i7-10700 (UHD 630 GPU) with 1920x1080
size:

$ glmark2 -s 1920x1080

I get a score of 665 (fvwm2, picom compositor disabled). This seems to
be right in the middle of reported results of other configurations with
UHD 630 graphics [1].

I can't figure out where '-O0' in the build comes from, for example:

[10/140] c++ -Isrc/libcommon-gl.a.p -Isrc -I../glmark2-2021.02/src -I../glmark2-2021.02/src/scene-ideas -I../glmark2-2021.02/src/scene-terrain -I../glmark2-2021.02/src/glad/include -I../glmark2-2021.02/src/libmatrix -I/usr/local/include -I/usr/local/include/libpng16 -I/usr/X11R6/include -fcolor-diagnostics -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wnon-virtual-dtor -std=c++14 -O0 '-DGLMARK_VERSION="2021.02"' '-DGLMARK_DATA_PATH="/usr/local/share/glmark2"' -O2 -pipe -fPIC -DUSE_EXCEPTIONS -DGLMARK2_USE_GL -MD -MQ src/libcommon-gl.a.p/libmatrix_mat.cc.o -MF src/libcommon-gl.a.p/libmatrix_mat.cc.o.d -o src/libcommon-gl.a.p/libmatrix_mat.cc.o -c ../glmark2-2021.02/src/libmatrix/mat.cc

I looked through the meson.build files and meson.port.mk, to no avail.

It comes with man pages glmark2(1) and glmark2-es2(1).

ok?

[1] https://openbenchmarking.org/test/pts/glmark2