buildman: Add -C option to force a reconfigure for each commit

Normally buildman wil try to configure U-Boot for a particular board on the
first commit that it builds in a series. Subsequent commits are built
without reconfiguring which normally works. Where it doesn't, buildman
automatically reconfigures and retries.

To fully emulate the way MAKEALL works, we should have an option to disable
this optimisation.

Add a -C option to cause buildman to always reconfigure on each commit.

Signed-off-by: Simon Glass <sjg@chromium.org>
buildman: Support in-tree builds

At present buildman always builds out-of-tree, that is it uses a separate
output directory from the source directory. Normally this is what you want,
but it is important that in-tree builds work also. Some Makefile changes may
break this.

Add a -i option to tell buildman to use in-tree builds, so that it is easy
to test this feature.

Signed-off-by: Simon Glass <sjg@chromium.org>
patman: make "No recipient" checking more tolerant

If Series-to tag is missing, Patman exits with a message
"No recipient".

This is just annoying for those who had already added
sendemail.to configuration.

I guess many developers have

  [sendemail]
          to = u-boot@lists.denx.de

in their .git/config because the 'To: u-boot@lists.denx.de' field
should always be added when sending patches.

That seems more reasonable rather than adding
'Series-to: u-boot@lists.denx.de' to every patch series.

Patman should exit only when both Series-to tag and sendemail.to
configuration are mising.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Simon Glass <sjg@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>
clang: workaround for generated constants

KBuild abuses the asm statement to write to a file and
clang chokes about these invalid asm statements. Hack it
even more by fooling this is actual valid asm code.
cc-option: make it work with clang

By default clang will return echo a warning if an option is unknown.
Therefore turn warnings into errors when polling for options.
Makefile: replace stat -c %s with wc

stat -c %s only works on a GNU host. Use wc instead.