qt5 5.3.1

Closes #30445.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>
qt5: update 5.3.1 bottle.
brew.rb: handle -—help for internal/external cmds.

Only display —-help for internal commands and not for external ones;
they can handle the flag themselves.

Closes #26675.
References #26755.
Closes #30300.
build libstxxl in release mode, fixes #30437
libstxxl: add 1.4.0 bottle.