Documentation: kunit: update kconfig options needed for UML coverage

Recent changes have made it so the current set is not sufficient.
Namely, CONFIG_DEBUG_INFO is not being set even when explicitly asked.

Specifying a version of the debug info fixes this.
Pick CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT as an option that's
hopefully less fragile (esp. given we're tied to GCC 6 and lower).

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Tested-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Documentation/dev-tools/kunit/running_tips.rst

@@ -114,6 +114,7 @@ Instead of enabling ``CONFIG_GCOV_KERNEL=y``, we can set these options:
 
 	CONFIG_DEBUG_KERNEL=y
 	CONFIG_DEBUG_INFO=y
+	CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
 	CONFIG_GCOV=y
 
 
@@ -122,7 +123,7 @@ Putting it together into a copy-pastable sequence of commands:
 .. code-block:: bash
 
 	# Append coverage options to the current config
-	$ echo -e "CONFIG_DEBUG_KERNEL=y\nCONFIG_DEBUG_INFO=y\nCONFIG_GCOV=y" >> .kunit/.kunitconfig
+	$ echo -e "CONFIG_DEBUG_KERNEL=y\nCONFIG_DEBUG_INFO=y\nCONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y\nCONFIG_GCOV=y" >> .kunit/.kunitconfig
 	$ ./tools/testing/kunit/kunit.py run
 	# Extract the coverage information from the build dir (.kunit/)
 	$ lcov -t "my_kunit_tests" -o coverage.info -c -d .kunit/