[cmake] Fixes to build on Silicon

[simogasp]

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Here are some fixes to build on Apple Silicon. They are mostly version bumps of the dependencies that have added support for the Silicon platform.

• bump geogram v1.7.6 -> v1.7.9
• bump png v1.6.35 -> 1.6.37
• some cmake adjustments to be platform independent

There are also some other bumps that I did not push yet:

• Tbb 2019_U6 -> v2021.3.0. It normally works, even for CCTag using the oneAPI branch (https://github.com/alicevision/CCTag/pull/178). But I don't know if there were other reasons for keeping the previous version
• for suitesparse no bump needed but for some reason I had to remove CC=${CMAKE_C_COMPILER} CXX=${CMAKE_CXX_COMPILER} from its build command line

[p12tic]

LGTM, I pretty much had to implement the same fixes in my own builds scripts that don't use ExternalProject_ADD.