change behavior of elfos.h slightly

[Jeffrey A Law]

  In message < 4.3.2.20000504114434.00e0bdb0@mail.lauterbach.com >you write:
  > >         LOCAL_LABEL_PREFIX: cause an error if this is not defined,
  > >         as it is required for correct local labels to be generated.
  > >
  > >         ASM_OUTPUT_INTERNAL_LABEL: use LOCAL_LABEL_PREFIX rather
  > >         than assuming one of ".".
  > >
  > >         ASM_GENERATE_INTERNAL_LABEL: Likewise.
  > >
  > >The latter two are required in order to be able to use elfos.h on
  > >e.g. MIPS and Alpha targets (assuming you want those targets to
  > >continue to use the "$" as their local label prefix).
  > 
  > I think you are heading in the wrong direction here. Though it might be a 
  > good idea to convert elfos.h to provide a default definition of 
  > LOCAL_LABEL_PREFIX and use it, you will still need to override the 
  > definitions in your target headers, because you can't define anything 
  > before including elfos.h. We want to get rid of the
  > 
  > #define SOMETHING
  > #include <someheader1.h>
  > #undef SOMETHING2
  > #include <someheader2.h>
Really?  I wasn't aware of that.

The style that we're trying to wean ports from is having one .h file
include some other .h file by instead listing them explicitly in the
desired order in configure.in.

We're trying to enforce it for new ports and when major reconstruction is
done for existing ports.  But we haven't forced every port to switch when
dealing with minor problems.

jeff