RFC: bump GCC requirement to 4.8

[laanwj]

Inspired by discussion here: #11722 (comment) . This would allow using more C++11 features such as thread local data (https://gcc.gnu.org/gcc-4.7/cxx0x_status.html versus https://gcc.gnu.org/gcc-4.8/cxx0x_status.html). FWIW gcc 4.7.0 was released in March 22, 2012, last bugfix release was 4.7.4 in June 12, 2014.

Also FWIW I tried to build bitcoin on g++ 4.7 a while ago and it was a pain; for example the AX_CXX_COMPILE_STDCXX fails because the __cplusplus macro is not set correctly, and that's only the beginning. As it's already effectively broken and no one else seems to even notice it, I wouldn't mind bumping the requirement to g++ 4.8 wholesale. But I'm not sure that discussion belongs here.

Is anyone successfully building on g++ 4.7?

@theuni what's your opinion?

[fanquake]

Release

GCC 4.8 was released March 22 2013, with it's most recent bug-fix release (4.8.5) on June 23 2015.
The GCC 4.8.x branch is no longer maintained. More info here: https://gcc.gnu.org/gcc-4.8/

C++11 Support

Status of C++11 support in GCC 4.8: https://gcc.gnu.org/gcc-4.8/cxx0x_status.html.
GCC 4.8.1 was the first feature-complete implementation of the 2011 C++ standard, previously known as C++0x.

From what I can find the last time we committed a fix specifically for GCC 4.7 was in #1126.
The last fix committed specifically for GCC 4.8 was in #3895.
There have been various "fixes" for wShadow warnings etc tested against GCC 4.8.x versions since then.

One of the downsides listed for "Consider building with -flto" in #10616 is "Before GCC 4.8: double size object files". A bump to GCC 4.8 would remove that issue.

[luke-jr]

• Debian: 6.3.0 (stable)
• Fedora: 7.2.1
• Gentoo: 5.4.0 (stable)
• RedHat/CentOS: 4.8.5
• Ubuntu: 4.8.2 (trusty)

So looks good to me.

[maflcko]

Since apparently no one uses gcc4.7 in daily (or regular) builds, I don't see a way how we could support that version. Even if we managed to get master compile with gcc4.7, it would likely end up breaking shortly after.

[sipa]

ACK on upping the requirement to GCC 4.8.

[meshcollider]

ACK on the bump too

[maflcko]

Anything left to do here? Can someone declare that it was bumped and close this issue?

[fanquake]

@MarcoFalke We should at least make it explicit in the docs. I'll open a PR.

[laanwj]

Also the build system needs to give a clear error message if the compiler version is known not supported. Currently it fails non-intuitively on AX_CXX_COMPILE_STDCXX w/ 4.7.
(bleh, that seems to be more difficult that you'd expect)