raco pkg {install,update}: add a `--auto' shorthand
make install: drop `-S' flag to `strip'

It turns out that no flags are standard, so don't try to use
any. That seems to be fine on the platforms that I tried.
fix (extracted part of) libunwind for x86_64

I had mixed up EBP vs. REG_EBP, etc., in extracting the x86_64 code.
remove unnecessary stack-unwind test

The test was meant to detect a bad traversal step, but it could unnecessarily
truncate the stack traversal when encountering recursive calls.
enable JIT stack trace on arity errors

On x86_64 Linux and Win64.