Move it to the top-level file to decide if we install/check
the generic headers or the arch specific headers.

This revealed a long standing bug where "make headers_check_all"
relied on the files in asm/ for the current architecture.
So make headers_check_all is now broken by this commit.

In addition:

o add a simpler way to detect if an arch support
  exporting header files.

o add 'set -e;' so we error out early if
  make headers_check_all fails.

o add sparc64 and cris to arch we do not process
  in make headers_*_all because:

    sparc64 - use sparc to export headers
    cris    - is know seriously broken

Includes suggestions from: David Woodhouse
<dwmw2@infradead.org>.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: David Woodhouse <dwmw2@infradead.org>