Revert "[cmake] Disable GCC lifetime DSE"

This reverts commit ce990b54.

This breaks some build bots - specifically when using GCC to build LLVM and
then -fno-lifetime-dse ends up passed to Clang in some tests like at
https://lab.llvm.org/buildbot/#/builders/139/builds/40594.

Bug: https://github.com/llvm/llvm-project/issues/24952
Bug: https://github.com/llvm/llvm-project/issues/57740

Differential Revision: https://reviews.llvm.org/D150505