it does not change the behavior of lsr,
but now only entry affine computations are considered
(except for injurong operations)

it fixes a rare bug where affine forms were smashed by
a exit computation.

SimplExpr: revised handling of nested conditional, `||`, `&&` expressions

Follow-up to ed89275cb.

AArch64, ARM, RISC-V and x86 ELF targets are changed.
PowerPC / ELF is unchanged because we use the EABI variant, which has
no `.data.rel.ro` section as far as I can see in GCC's output.
(The SVR4 variant has `.data.rel.ro` but does not have `.sdata2`,
which CompCert uses.)

Fixes: #454

Add the missing case for Sfoldr

Non-trapping loads which fail to match their annotation now return
Vundef instead of failing.
- [may_trap] can now returns false for non-trapping load even in the strict
  semantics. Hence non-trapping loads are not added in [ok_rsval].
- Allows the scheduler to move non-trapping loads above branches.
- Re-enable -fnontrap-loads by default.
- The simulation of the strict semantics by the lax one uses a less-def
  relation.