It's important to point out that the concept of "linking" is not mentioned in the GPL's definition of "Program" or "covered work", nor is it used as a determiner to decide if the viral nature applies to your work or not. That's a common misconception that people who've read about GPL but never read the actual license text have. I point that out here only because the developer here mentioned it, but it's irrelevant.
The viral nature applies if you "convey a work based on the Program, or the modifications to produce it from the Program" unless it is "a compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program" [0].
If that sounds vague enough to be interpreted in a lot of different ways to you, you're right. Even the FSF themselves admit it would be up to a court to decide[1] (which unfortunately in a lot of cases means whoever has the most money wins).
tl;dr - When in doubt, assume you need to make your work GPL too.
The viral nature applies if you "convey a work based on the Program, or the modifications to produce it from the Program" unless it is "a compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program" [0].
If that sounds vague enough to be interpreted in a lot of different ways to you, you're right. Even the FSF themselves admit it would be up to a court to decide[1] (which unfortunately in a lot of cases means whoever has the most money wins).
tl;dr - When in doubt, assume you need to make your work GPL too.
[0]: https://www.gnu.org/licenses/gpl-3.0.en.html
[1]: https://www.gnu.org/licenses/gpl-faq.html#MereAggregation