Minimum GCC version for building glibc

[Joseph Myers]

On Wed, 5 Nov 2014, Mike Frysinger wrote:

> we bump the min required version of any package for these reasons:
>  - newer functionality is not feasible to duplicate in glibc
>  - existing backwards compat code grows to a size that is too onerous to 
> keep maintaining

- There is a combinatorial explosion of possible feature combinations, so 
to make that more maintainable it makes sense to declare old versions 
unsupported and avoid even needing to think about whether a feature you're 
using existed in some old version few people will be using.

I think -Werror makes it more likely building with old versions will break 
when they aren't actively tested.  We also now have a clear use for 
diagnostic pragmas, new in 4.6, to allow more selective disabling of 
particular warnings together with -Werror.

> in this case, the proposal of raising gcc 4.4 to 4.7 was accompanied by "it 
> might make implementing C11 support easier".  it seems like support for that was 
> already posted not requiring 4.7.  so what's the reason for dropping 4.4/4.5 ?

Having two different ways to implement atomics on the same architecture, 
unless justified by variations in hardware support, is another 
contribution to that combinatorial explosion of configurations.  Once 
we're happy use of __atomic_* works well on any given architecture, I 
think it should replace the old approach there (and so require 4.7 there) 
rather than keeping an old and little-used alternative for building with 
older compilers.

-- 
Joseph S. Myers
joseph@codesourcery.com