Auto merge of #3018 - ehuss:highfive-triagebot, r=JohnTitor

Migrate from highfive to triagebot

This migrates this repository from using the highfive bot to using triagebot (aka rustbot).

This should not be merged without coordinating the removal of the highfive webhook and/or merging rust-lang/highfive#433.

triagebot.toml

@@ -3,4 +3,23 @@ allow-unauthenticated = [
     "C-*", "O-*", "S-*"
 ]
 
+[autolabel."S-waiting-on-review"]
+new_pr = true
+
 [assign]
+contributing_url = "https://github.com/rust-lang/libc/blob/master/CONTRIBUTING.md"
+
+[assign.owners]
+"*" = ["@JohnTitor"]
+
+[mentions."src/unix/bsd/netbsdlike/openbsd"]
+message = "Some changes occurred in OpenBSD module"
+cc = ["@semarie"]
+
+[mentions."src/unix/bsd/netbsdlike/mod.rs"]
+message = "Some changes occurred in OpenBSD module"
+cc = ["@semarie"]
+
+[mentions."src/unix/solarish"]
+message = "Some changes occurred in solarish module"
+cc = ["@jclulow", "@pfmooney"]