Merge #561: Respect LDFLAGS and #undef STATIC_PRECOMPUTATION if using basic config

dbed75d Undefine `STATIC_PRECOMPUTATION` if using the basic config (DesWurstes)
310111e Keep LDFLAGS if `--coverage` (DesWurstes)

Pull request description:

  Update: **This is a trimmed pull request with strong rationale.**

  - Adding `--coverage` shouldn't reset `LDFLAGS`, this is definitely a typo
  - The basic configuration should undefine `STATIC_PRECOMPUTATION`, as generating it is not supported and it complicates #549

Tree-SHA512: 29f0dd4c870ec60d535346446b453da459ca843ed1265c2bc966bf0fcbdf3c5c79f9e48a419662e81d790a7003f8877a16e2a5a74aa5c0b79645e15ad56a0f66