doctor: add check for osx-gcc-installer

This might not detect all cases, but should detect the two most
common ones.
rust: --HEAD uses incoming branch, not master

Closes #20409.

Signed-off-by: Samuel John <github@SamuelJohn.de>
git 1.8.3.1

Closes #20402.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
sqlite: fix download filename of functions

Closes #20412.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
Dart 23799

Closes #20411.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>