[Development] HEADS UP: OSX build requirements for 5.7

[Tim Blechmann]

>> we have seen funny toolchain bugs, with 10.10 sdk and 10.8 deployment
>> target on 10.8, where std::exceptions could not be caught ... compiling
>> against 10.8 sdk solved that issue.
> 
> Regardless of whether that is a valid approach or not, the fact that people 
> are doing that poses a problem for us. If we write code against the latest 
> toolchain, it may not compile against older ones people might be using.

this implies bumping the minimum requirements. for some use cases this
might be acceptable, for others it isn't.


> That can be because we used new features that aren't present in older ones, 
> even if properly runtime checked.
> 
> Another problem is that the compilers in the old toolchains are older, with 
> older libc++ and with bugs that we aren't testing for.

... or newer toolchains can introduce regressions ...


> If we're going to upgrade our Xcode in all our builds, I would advise we also 
> make it mandatory for everyone else too. Check during configure against the 
> minimum SDK version, that being the *current* at the time of release.

so what happens when you are hit by a toolchain regression? i'm not
voting for having code compiling with gcc-4.2 or any of the llvm-gcc
flavors which were around during that time. however qt is a framework
and it should support more than one toolchain so that people who are hit
by toolchain bugs still have an alternative ...

cheers,
tim