kunit: tool: Enable CONFIG_FORTIFY_SOURCE under UML

Since commit ba38961a ("um: Enable FORTIFY_SOURCE"), it's possible
to run the FORTIFY tests under UML. Enable CONFIG_FORTIFY_SOURCE when
running with --alltests to gain additional coverage, and by default under
UML.
Signed-off-by: Kees Cook <keescook@chromium.org>

tools/testing/kunit/configs/all_tests.config

@@ -9,6 +9,8 @@ CONFIG_KUNIT=y
 CONFIG_KUNIT_EXAMPLE_TEST=y
 CONFIG_KUNIT_ALL_TESTS=y
 
+CONFIG_FORTIFY_SOURCE=y
+
 CONFIG_IIO=y
 
 CONFIG_EXT4_FS=y

tools/testing/kunit/configs/arch_uml.config

@@ -3,3 +3,6 @@
 # Enable virtio/pci, as a lot of tests require it.
 CONFIG_VIRTIO_UML=y
 CONFIG_UML_PCI_OVER_VIRTIO=y
+
+# Enable FORTIFY_SOURCE for wider checking.
+CONFIG_FORTIFY_SOURCE=y