[lldb/Commands] Add ability to run shell command on the host.
This patch introduces the (-h|--host) option to the platform shell
command. It allows the user to run shell commands from the host platform
(always available) without putting lldb in the background.
Since the default behaviour of platform shell is to run the command of
the selected platform, having such a choice can be quite handy when
debugging remote targets, for instances.
This patch also introduces a shell alias, to improve the command
discoverability and make it more convenient to use for the user.
Differential Revision: https://reviews.llvm.org/D79659
Signed-off-by: Med Ismail Bennani <email@example.com>