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
.
Signed-off-by: Sam Ravnborg 
Cc: David Woodhouse