Tests: Test add_custom_command and add_custom_target error cases

Add RunCMake.add_custom_command and RunCMake.add_custom_target tests to
cover the error messages for these commands.
Merge topic 'test-custom-command-errors' into next

39baf728 Tests: Test add_custom_command and add_custom_target error cases
Rename doing_verbatim to doing_nothing

We are about to introduce another property here, so give this
a better name.
Introduce USES_TERMINAL property for add_custom_{command,target}

This property tells the generator to give the command direct access to the
terminal if possible.
Give the interactive cache editor the USES_TERMINAL property
Ninja: factor out the test for console pool support
Ninja: Remove unused declaration
Ninja: Implement USES_TERMINAL using the console pool if available
Help: Add notes for topic 'console-pool'
Merge topic 'console-pool' into next

8b59dde6 Help: Add notes for topic 'console-pool'
ce2fe7c8 Ninja: Implement USES_TERMINAL using the console pool if available
80c5690b Ninja: Remove unused declaration
0f0eaf3f Ninja: factor out the test for console pool support
4897e25e Give the interactive cache editor the USES_TERMINAL property
d12a8443 Introduce USES_TERMINAL property for add_custom_{command,target}
ad6ee426 Rename doing_verbatim to doing_nothing