[Makefile] change visibility to default
[Makefile] change visibility to default

Such that backtrace can extract the function symbols

hostilefork/rebol,codebybrett/ren-c,rgchris/ren-c,draegtun/ren-c,codebybrett/ren-c,codebybrett/ren-c,rgchris/ren-c,draegtun/ren-c,mbk/ren-c,hostilefork/rebol,rgchris/ren-c,codebybrett/ren-c,rgchris/ren-c,hostilefork/rebol,draegtun/ren-c,giuliolunati/ren-c,kealist/ren-c,hostilefork/rebol,kealist/ren-c,kealist/ren-c,mbk/ren-c,giuliolunati/ren-c,kealist/ren-c,kealist/ren-c,hostilefork/rebol,hostilefork/rebol,draegtun/ren-c,kealist/ren-c,codebybrett/ren-c,giuliolunati/ren-c,giuliolunati/ren-c,mbk/ren-c,giuliolunati/ren-c,draegtun/ren-c,mbk/ren-c,codebybrett/ren-c,draegtun/ren-c,rgchris/ren-c