WARNING: Requires C++17 'guaranteed copy elision' to fix ambiguous
operator problems in Variant.
This was added for this commit (and future C++17 uses) in #36457.
Xcode 10+ is needed for exhaustive C++17 support (gnu++17).
11.3 is the latest available version on Travis, and we don't have a
specific reason not to use it.
Follow-up to #36457.
It's now available and allows us to have a better default environment,
with GCC 7.4.0 and Clang 7.
We now need GCC 7+ for C++17 support so it's more efficient to upgrade
the image than to install it on Ubuntu 16.04 (xenial).
Also fixes a couple -Wdeprecated-declarations warnings on macOS now
that we build against macOS 10.12.
As per #36436, we now need C++17's guaranteed copy elision feature to
solve ambiguities in Variant.
Core developers discussed the idea to move from C++14 to C++17 as our
minimum required C++ standard, and all agreed. Note that this doesn't
mean that Godot is going to be written in "modern C++", but we'll use
modern features where they make sense to simplify our "C with classes"
codebase. Apart from new code written recently, most of the codebase
still has to be ported to use newer features where relevant.
Proper support for C++17 means that we need recent compiler versions:
- GCC 7+
- Clang 6+
- VS 2017 15.7+
Additionally, C++17's `std::shared_mutex` (conditionally used by
`vk_mem_alloc.h` when C++17 support is enabled) is only available in
macOS 10.12+, so we increase our minimum supported version.
In the vast majority of cases, this will be a false positive error
thrown by Vulkan-Loader when a Linux system has Vulkan ICDs for both
32-bit and 64-bit. The error is of the form:
```
ERROR: [Loader Message] Code 0 : /usr/lib/libvulkan_intel.so: wrong ELF class: ELFCLASS32
ERROR: [Loader Message] Code 0 : /usr/lib/libvulkan_radeon.so: wrong ELF class: ELFCLASS32
```
The loader dlopen's the 32-bit ICDs first, raises this error, and then
happily goes on to try and use the 64-bit ICDs.
Upstream report: https://github.com/KhronosGroup/Vulkan-Loader/issues/262Fixes#36185.
On GCC and Clang, we use C11 and C++14 with GNU extensions (`std=gnu11`
and `std=gnu++14`). Those are the defaults for current GCC and Clang,
and also match the feature sets we want to use in Godot.
On MSVC, we require C++14 support explicitly with `/std:c++14`, and
make it strict with the use of `/permissive-` (so features of C++17 or
later can't be used).
Moves the definition before querying environment flags and platform
config so that it can be overridden when necessary.
