Log Message:
nim: Update to 1.6.8

Noteworthy changes from 1.6.6:

- Fixed "Add --gc:arc (or --mm:arc) induce different behavior when using
  converter" (#19862)
- Fixed "Converting unsigned integer to float fails in VM" (#19199)
- Fixed "regression(0.20.0 => devel): var params assignment gives silently
  wrong results in VM" (#15974)
- Fixed "genDepend broken for duplicate module names in separate folders"
  (#18735)
- Fixed "Orc booting compiler doesn't work with newSeq operations" (#19404)
- Fixed "hasCustomPragma and getCustomPragmaVal don't work on fields with
  backticks" (#20067)
- Fixed "Cant use uint64 in case" (#20031)
- Fixed "nim jsondoc output is broken" (#20132)
- Fixed "Underscores are unnecessarily escaped in db_mysql" (#20153)
- Fixed "Invalid codegen when block ends with lent" (#20107)
- Fixed "locals doesn't work with ORC" (#20162)
- Fixed "reset does not work on set" (#19967)
- Fixed "selectRead and selectWrite are dangerous to use sockets with FD
  numbers bigger than FD_SETSIZE (1024) on *nixes" (#19973)
- Fixed "use-after-free bugs in object variants" (#20305)
- Fixed "[ARC] C compiler error when using the result of a template in the
  subscript operator" (#20303)
- Fixed "Calling nullary templates without () doesn't work inside calls
  inside other templates" (#13515)
- Fixed "[Regression] Incorrect captures of pegs \ident macro in nim 1.6"
  (#19104)
- Fixed "Windows gcc shipped with choosenim 1.6.4 with TLS emulation turned
  off : The application was unable to start correctly (0xc000007b)."
  (#19713)