On macOS QDir::tempPath() falls back to a hardcoded /tmp path if $TMPDIR is empty

On macOS, if a process is launched via sudo with an empty $TMPDIR environment variable, QDir::tempPath() falls back to a hardcoded "/tmp" path, which might not be writable.

Correct writable temporary directory can be obtained via call to NSTemporaryDirectory()

Sample program is attached. It's output is below:
1. Normal execution
Qt tempPath: /var/folders/3z/jqb49r_56xz_ky8fqb55ccnh0000gn/T
Cocoa tempPath: /var/folders/3z/jqb49r_56xz_ky8fqb55ccnh0000gn/T/

2. sudo execution
Qt tempPath: /tmp
Cocoa tempPath: /var/folders/zz/zyxvpxvq6csfxvn_n0000000000000/T/