Documentation: update SubmitChecklist for O=objdir and kconfig testing

Add build testing using 'O=builddir'.

Add build testing with various kconfig symbols disabled, listing
common ones that are known to cause build problems.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/SubmitChecklist

@@ -18,6 +18,8 @@ kernel patches.
 
 2b: Passes allnoconfig, allmodconfig
 
+2c: Builds successfully when using O=builddir
+
 3: Builds on multiple CPU architectures by using local cross-compile tools
    or some other build farm.
 
@@ -95,3 +97,13 @@ kernel patches.
 
 25: If any ioctl's are added by the patch, then also update
     Documentation/ioctl/ioctl-number.txt.
+
+26: If your modified source code depends on or uses any of the kernel
+    APIs or features that are related to the following kconfig symbols,
+    then test multiple builds with the related kconfig symbols disabled
+    and/or =m (if that option is available) [not all of these at the
+    same time, just various/random combinations of them]:
+
+    CONFIG_SMP, CONFIG_SYSFS, CONFIG_PROC_FS, CONFIG_INPUT, CONFIG_PCI,
+    CONFIG_BLOCK, CONFIG_PM, CONFIG_HOTPLUG, CONFIG_MAGIC_SYSRQ,
+    CONFIG_NET, CONFIG_INET=n (but latter with CONFIG_NET=y)