How to Build Latest HandBrake on linux with FDO (PGO) + LTO?

Passing CFLAGS and CXXFLAGS to a HandBrake build for the latest version (v1.3.3 at the time of this writing) will work until you add -flto which will **FAIL** the whole build. How to build HandBrake with LTO option -flto and as a stretch goal, with FDO as well (feedback directed optimisation aka FDO aka PGO)? Most of the codecs within HandBrake are developed with "hand-coded" assembly, so many assert that the compiler optimisation gains would not be that much. I would like to test and challenge that assertion!