[Toybox] pathological case in sed s///g

[makepost at firemail.cc]

> wouldn't it be better to have more stuff along the lines of clang's
> __has_builtin/__has_feature/__has_include? they're already very useful
> for getting rid of this kind of stuff, and a __has_function would
> cover most of what's missing.

Feature claims of clang and musl are giving us a conflict when building cmake btw, could anyone look at https://github.com/gentoo/musl/issues/141 please? I don't know whether to forward this to clang or musl or cmake or some other list, thus glad you brought up the topic.