doc: gsg: macOS: Describe Gatekeeper workarounds

Describe how to work around the Gatekeeper enforcement of security
policies in apps launched from the Terminal.

Fixes zephyrproject-rtos#23168.

Signed-off-by: Carles Cufi <[email protected]>

doc/getting_started/installation_mac.rst

@@ -7,8 +7,8 @@ This section describes how to set up a Zephyr development environment on macOS.
 
 These instructions have been tested on the following macOS versions:
 
-* Mac OS X 10.11 (El Capitan)
-* macOS Sierra 10.12
+* macOS 10.14 Mojave
+* macOS 10.15 Catalina
 
 Update Your Operating System
 ****************************
@@ -47,8 +47,38 @@ Now install these host dependencies with the ``brew`` command:
 
 .. _Homebrew site: https://brew.sh/
 
+.. _mac-gatekeeper:
+
+Important note about Gatekeeper
+*******************************
+
+Starting with macOS 10.15 Catalina, applications launched from the macOS
+Terminal application (or any other terminal emulator) are subject to the same
+system security policies that are applied to applications launched from the
+Dock. This means that if you download executable binaries using a web browser,
+macOS will not let you execute those from the Terminal by default. In order to
+get around this issue you can take two different approaches:
+
+* Run ``xattr -r -d com.apple.quarantine /path/to/folder`` where
+  ``path/to/folder`` is the path to the enclosing folder where the executables
+  you want to run are located.
+
+* Open "System Preferences" -> "Security and Privacy" -> "Privacy" and then
+  scroll down to "Developer Tools". Then unlock the lock to be able to make
+  changes and check the checkbox corresponding to your terminal emulator of
+  choice. This will apply to any executable being launched from such terminal
+  program.
+
+Note that this section does **not** apply to executables installed with
+Homebrew, since those are automatically un-quarantined by ``brew`` itself. This
+is however relevant for most :ref:`third_party_x_compilers`.
+
+.. _macOS Gatekeeper: https://en.wikipedia.org/wiki/Gatekeeper_(macOS)
+
 Additional notes for MacPorts users
 ***********************************
 
-While MacPorts is not officially supported in this guide, it is possible to use MacPorts instead of Homebrew to get all the required dependencies on macOS.
-Note also that you may need to install ``rust`` and ``cargo`` for the Python dependencies to install correctly.
+While MacPorts is not officially supported in this guide, it is possible to use
+MacPorts instead of Homebrew to get all the required dependencies on macOS.
+Note also that you may need to install ``rust`` and ``cargo`` for the Python
+dependencies to install correctly.