Revert "Reland "[CMake] Bumps minimum version to 3.20.0.""

This reverts commit 65429b9af6a2c99d340ab2dcddd41dab201f399c.

Broke several projects, see https://reviews.llvm.org/D144509#4347562 onwards.

Also reverts follow-up commit "[OpenMP] Compile assembly files as ASM, not C"

This reverts commit 4072c8aee4c89c4457f4f30d01dc9bb4dfa52559.

Also reverts fix attempt  "[cmake] Set CMP0091 to fix Windows builds after the cmake_minimum_required bump"

This reverts commit 7d47dac5f828efd1d378ba44a97559114f00fb64.

GitOrigin-RevId: d763c6e5e2d0a6b34097aa7dabca31e9aff9b0b6
1 file changed