compiler standards (and/or min gcc version) supported with installed headers ?

[Andreas Jaeger]

Here're some minor changes. Please review whether the language itself is 
clear,

Andreas

* glibc needs a recent GCC compiler version to build itself (right now
   at least 4.3 required, 4.6 or newer recommended)

* Userland applications and libraries that use glibc's headers and
   libraries can be build by a variety of compilers with the following
   notes:

   - The installed headers should work with any compiler that:
     * supports at least ISO C 90 (or C++98)
     * supports the type "long long"
   - GCC version 2.95.3 is the oldest compiler supported in general
     (for some more recent hardware architectures a more recent
     compiler will be needed)
   - Compiler dependend code needs to be protected by proper feature
     test macros. For example the various GCC __builtin_X functions can
     be used but need to be properly guarded.
   - The glibc header files might include special optimizations for
     newer compiler versions which might not be available for older
     compilers
   - The header files for glibc use GCC 4.3 as baseline for
     optimizations
   - Support for other compilers besides GCC might need extra patches
     which are welcome to be submitted for inclusion glibc
   - For headers shared with gnulib, other conditions do apply (the
     requirements from gnulib to support even older compilers)

To support different compilers, we would ideally not test - as today -
for a specific GCC version but for a specific feature.

So, instead of __GNUC_PREREQ(x,y) to check for a specific version in
some header file, the advise is to add a macro to features.h, like
__GLIBC_HAVE_BUILTIN_COMPLEX and use that - and that macro definition
is dependend on compiler versions.

-- 
  Andreas Jaeger aj@{suse.com,opensuse.org} Twitter/Identica: jaegerandi
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