Minimum compiler versions

[Nicolás Alvarez]

Hello devs,

Currently our Policies wiki page[1] says the minimum supported
compilers for KF5 are gcc 4.5, clang 3.1 and MSVC 2010.

Due to the use of range-based for loops, ThreadWeaver doesn't compile
on MSVC2010 or gcc4.5. kcoreaddons doesn't build on gcc 4.5 because it
uses nullptr. More testing to come.

I think the KDE-Windows people discussed dropping MSVC2010 support at
Akademy 2014. Is there any specific reason/rationale why gcc 4.5 was
declared the minimum, such as being the default compiler in an old
distro we'd like to support? Would people be willing to drop support
for gcc 4.5?

If we'll keep the compiler requirements as-is, I volunteer to fix
what's broken in the minimum versions we claim to support. But I think
we need CI for gcc 4.5, otherwise it will keep breaking...

[1] https://community.kde.org/Frameworks/Policies

-- 
Nicolás