kunit: add coverage_uml.config to enable GCOV on UML

Now that kunit.py's --kunitconfig is repeatable, let's create a file to
hold the various options needed to enable coverage under UML.

This can be used like so:
$ ./tools/testing/kunit/kunit.py run \
--kunitconfig=tools/testing/kunit/configs/all_tests_uml.config \
--kunitconfig=tools/testing/kunit/configs/coverage_uml.config \
--make_options=CC=/usr/bin/gcc-6

which on my system is enough to get coverage working [1].

This is still a clunky command, but far better than before.

[1] at the time of this commit, I get:
Overall coverage rate:
lines......: 11.6% (34112 of 295033 lines)
functions..: 15.3% (3721 of 24368 functions)

Signed-off-by: Daniel Latypov <[e-mail]>
Reviewed-by: David Gow <[e-mail]>
Reviewed-by: Brendan Higgins <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

Documentation/dev-tools/kunit/running_tips.rst

···
 .. code-block:: bash
 
 	# Append coverage options to the current config
-	$ 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
+	$ ./tools/testing/kunit/kunit.py run --kunitconfig=.kunit/ --kunitconfig=tools/testing/kunit/configs/coverage_uml.config
 	# Extract the coverage information from the build dir (.kunit/)
 	$ lcov -t "my_kunit_tests" -o coverage.info -c -d .kunit/
 

tools/testing/kunit/configs/coverage_uml.config

···
+# This config fragment enables coverage on UML, which is different from the
+# normal gcov used in other arches (no debugfs).
+# Example usage:
+# ./tools/testing/kunit/kunit.py run \
+#   --kunitconfig=tools/testing/kunit/configs/all_tests_uml.config \
+#   --kunitconfig=tools/testing/kunit/configs/coverage_uml.config
+
+CONFIG_DEBUG_KERNEL=y
+CONFIG_DEBUG_INFO=y
+CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
+CONFIG_GCOV=y