Users like desktop-shell want to parse a provided string containing a
combination of environment and arg, e.g.: ENV=stuff /path/to/thing --good
Add support to custom-env for parsing this, with tests, so we can delete
the custom implementation inside desktop-shell.
Signed-off-by: Daniel Stone <daniels@collabora.com>
execve() takes the same form for arguments as environment: an array of
constant pointers to mutable strings, terminated by a NULL.
To make it easier for users who want to build up their own argument
strings to pass to execve, add support for argument arrays to custom_env.
Signed-off-by: Daniel Stone <daniels@collabora.com>
Test the basic stuff: initialising from a known environment, setting a
new variable, overwriting a previous variable, and getting the resulting
array to pass to execve.
Signed-off-by: Daniel Stone <daniels@collabora.com>
