win64: use a GlobalVariable in the .text section for debuginfo, rather than hacking the MCJIT MemoryManager
fix issues with last commit on legacy platforms
showdict: use endof instead of sizeof

Sometimes, the output showed the truncation mark "…" even
when nothing was truncated.
Merge pull request #9463 from JuliaLang/rf/dict-show-utf8

showdict: use endof instead of sizeof