This allows users to overrule a module from command line.
As example, the Zephyr build system loads the module FOO from
`modules/FOO`, but user has a custom FOO locally at `custom/FOO` and
would like to use this module instead of manifest specified.
If user does `-DZEPHYR_EXTRA_MODULES=custom/FOO` the following error
will be seen:
```
The binary directory
build/modules/FOO
is already used to build a source directory. It cannot be used to build
source directory
custom/FOO
Specify a unique binary directory name.
```
Removing duplicates from the list allows a user to use
`-DZEPHYR_EXTRA_MODULES=custom/FOO` and thus replace `modules/FOO` for
the current build.
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>
2bf26ecf4d