shadow header success

[Nathan Myers <ncm at cantrip dot org>]

This is to report an initial success with shadow headers.  Having 
constructed a set of shadows, under cshadow/, of files included by 
standard headers in /usr/include etc., as described in the previous 
posting, I was able to build a "hello world" program using them with 
the command line:

  v3/bin/g++ -D_ISOC9X_SOURCE -I gcc/libstdc++-v3/shadow 
     -I build/i686-pc-linux-gnu/libstdc++-v3/cshadow hello.c

The only oddity was the need for the -D option, arising from the
(re-)definition of std::fprintf() found in shadow/bits/std_cstdio.h.

The work left to do to make them all play nice includes:

  - additions to configure.in to discover 
  
    - bogus header names to tell inclosure to ignore, based on 
      the target build environment identified (e.g. machine/ansi.h
      on Linux/x86/glibc), and  

    - the directories searched by the compiler, in addition to ours, 
      to pass to the inclosure script. This must identify header 
      directories looked at by the _target_ compiler.

  - additions to configure.in to handle a flag --enable-shadow-headers.

  - additions to Makefile.am to build the cshadow/ directory, if
    that flag is set, and additions to install the shadow/ and cshadow/
    trees under the --prefix tree.

  - cleaning up use of pathnames and temp files in the scripts 
    inclosure and mkcshadow.

  - adding shadow declarations for non-ISO extensions to standard
    headers under shadow/ and shadow/bits/, such as the POSIX and 
    XOPEN extensions (girded about with "#ifdef __USE_*" directives as 
    appropriate).

Nathan Myers
ncm at cantrip dot org