[Core] Update C standard to GNU11, C++ to GNU++14

[KarlK90]

Description

Pushes the used C standard for QMK to GNU11 and C++ standard to GNU17.

GCC support on QMK platfroms

Platform	AVR GCC Version	Embedded ARM GCC Version	AMD64 GCC Version
Windows	8.4.0 (MSYS2)	10.1 (MSYS2)	11.3.0 (MSYS2)
MacOS	8.4.0 (Homebrew)	8.4.0 (Homebrew)	12.1.0 (Homebrew)
FreeBSD	11.2.0 (12 + 13)	8.4.0 (12) 11.3.0 (13)	12.1.0 (13) 11.2.0 (12)
WSL2	8.3.0 (QMK base container)	8.3.1 (QMK base container)	10.2.1 (QMK base container)
Arch	12.1.0 (Arch Packages)	12.1.0 (Arch Packages)	12.1.0 (Arch Packages)
Manjaro	12.1.0 (Arch Packages)	12.1.0 (Arch Packages)	12.1.0 (Arch Packages)
Fedora	12.2.0 (36), 11.1.0 (35), 10.2.0 (34)	11.1.0 (36) 11.1.0 (35) 10.2.0 (34)	12.0.1 (36) 11.2.1 (35) 11.0.1 (34)
Ubuntu	5.4.0 (22.04 LTS + 20.04 LTS + 18.04 LTS)	10.3.0 (22.04 LTS) 9.2.1 (20.04 LTS) 6.3.1 (18.04 LTS)	11.2.0 (22.04 LTS) 9.3.0 (20.04 LTS) 7.3.0 (18.04 LTS)
Debian	5.4.0 (Sid + 11 + 10)	10.3.0 (Sid) 8.3.1 (11) 7.3.1 (10)	11.2.0 (Sid) 10.2.1 (11) 8.3.0 (10)
Gentoo	10.3.0+ (sys-devel/gcc)	10.3.0+ (sys-devel/gcc)	10.3.0+ (sys-devel/gcc)
Sabayon	10.3.0+ (sys-devel/gcc)	10.3.0+ (sys-devel/gcc)	10.3.0+ (sys-devel/gcc)
openSUSE Tumbleweed	5.4.0 (Experimental) / 6.5.0 (Community)	12.1.1	12.1.1
openSUSE Leap 15.3	10.3.0 (Community)	12.1.1	12.1.1
Slackware	10.2.0 (15.0)	10.2.0 (15.0)	11.3.0
Solus	8.3.0	8.3.0	11.3.0
Void	9.3.0	9.3.0	10.2.1

Target	Minimum version	QMK CI
AMD64	7.3.0	10.2.1
AVR	5.4.0	8.3.0
ARM	6.3.1	8.3.1

Lang. standard	GCC support
C11	4.9+ (complete)
C17	8.1+ (complete)
C++14	5.x+ (complete)
C++17	8.x+ (complete)
C++20	11.x+ (partial)
C++23	12.x+ (partial)

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Part of [Core] Add Raspberry Pi RP2040 support #14877

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[zvecr]

It would be nice to get some insight into potential impact, like was handled in #7920. Slightly more complicated, due to needing to check avr/arm/native compiler versions?

[tzarc]

Probably worth bumping C++ standard, too.

[KarlK90]

Isn't c++ already on gnu11?

[tzarc]

I thought we discussed going to 14 on one of your previous PRs for unit tests?

[KarlK90]

I thought we discussed going to 14 on one of your previous PRs for unit tests?

Ah yes, even 17 if I remember correctly. How are the constraints regarding default OS availability here? I suspect that somebody who is able to write a unit-test should be able to update to a recent GCC version.

[KarlK90]

I have updated the GCC compatibility table to cover AVR, ARM and AMD64 targets for all QMK platforms. We can safely update to GNU11 for C and GNU14 for C++.

The only CPP code which is not test code is the USB HID converter which is used by converters like the adb_usb and usb_usb converters. We could upgrade the test code to GNU17 and potentially use new language features in the tests. This should be possible as the testes are run by the CI and experienced users which should have a up to date GCC by default on most distros. The CPP standard for AVR/ARM/RISC-V targets would remain at GNU14 as the minimum AVR compiler version is 5.4.0.