As mentioned by @Huang and linked by @DBS here: https://stackoverflow.com/a/38452396/10594231

This could be fixed by appending the unicode variation selector VS15 to the character which forces it to be rendered as text rather than emoji.

div.entry-content p a::before {
    content: "\2197";
    padding-right: 2px
}

would become

div.entry-content p a::before {
    content: "\2197\FE0E";
    padding-right: 2px
}