Also enable some tests that were disabled for no apparant reason.
(The comment in zst.rs was wrong, the test was disabled also for miri execution.)
Delete env_args test as the args can actually be queried with MIR-libstd (currently, they are always empty)
Thanks to the `Value` locals refactoring, now primitive locals (ints,
floats, chars, bools, and the like) will not require `Allocation`s at
all, and locals that are never initialized at all because of conditional
control flow won't be wasting memory.
previously we moved to the target block *before* calling a function, so when inspecting
the stack, it appeared as if we were in the first statement of the next block.
