Correct OQS_MINIMAL_BUILD logic when introducing new optimizations

[baentsch]

The implementation of this feature is brittle when new optimizations/cmake-subtargets are introduced (as was the case with #1117): Using the feature then leads to "strange" performance drops (vs. building all algorithms without this build option):

liboqs/.CMake/alg_support.cmake

Line 672 in 6888e9e

# Case 3, platform specific

implements effectively a white-list of cmake-build sub-targets that needs extension when adding new optimization targets. Maybe another way to handle this would be better (though can't think of one myself given a lack of understanding of cmake). Otherwise, this issue is to remind future implementors of new optimizations to add them at the above code location.