Fix compilation errors with C++20 (#4098)

### What
* Closes #4090

I tried getting these tests running on CI too, but after 2h I gave up.
Andreas has volunteered to try a bit more, so let's hold off merging
this PR until we can reproduce the problems on CI.
See #4097 if you dare

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/4098) (if
applicable)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG

- [PR Build Summary](https://build.rerun.io/pr/4098)
- [Docs
preview](https://rerun.io/preview/a69d06b8a84b78469192f341bebdfc32dc7936cc/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/a69d06b8a84b78469192f341bebdfc32dc7936cc/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://ref.rerun.io/dev/bench/)
- [Wasm size tracking](https://ref.rerun.io/dev/sizes/)

CMakeLists.txt

@@ -36,6 +36,8 @@ function(set_default_warning_settings target)
         if(CMAKE_CXX_COMPILER_ID MATCHES "Clang") # match both "Clang" and "AppleClang"
             target_compile_options(${target} PRIVATE
                 -Wc++17-compat-pedantic
+                -Wc++20-compat-pedantic
+                -Wpre-c2x-compat-pedantic
                 -Wc99-extensions
                 -Wgnu
                 -Wnon-gcc

rerun_cpp/src/rerun/datatypes/quaternion_ext.cpp

@@ -13,32 +13,34 @@ namespace rerun {
 
         /// Construct Quaternion from x/y/z/w values.
         static Quaternion from_xyzw(float x, float y, float z, float w) {
-            return Quaternion{x, y, z, w};
+            return Quaternion::from_xyzw({x, y, z, w});
         }
 
         /// Construct Quaternion from w/x/y/z values.
         static Quaternion from_wxyz(float w, float x, float y, float z) {
-            return Quaternion{x, y, z, w};
+            return Quaternion::from_xyzw(x, y, z, w);
         }
 
         /// Construct Quaternion from x/y/z/w array.
         static Quaternion from_xyzw(std::array<float, 4> xyzw_) {
-            return Quaternion{xyzw_};
+            Quaternion q;
+            q.xyzw = xyzw_;
+            return q;
         }
 
         /// Construct Quaternion from w/x/y/z array.
         static Quaternion from_wxyz(std::array<float, 4> wxyz_) {
-            return Quaternion{wxyz_[1], wxyz_[2], wxyz_[3], wxyz_[0]};
+            return Quaternion::from_xyzw(wxyz_[1], wxyz_[2], wxyz_[3], wxyz_[0]);
         }
 
         /// Construct Quaternion from x/y/z/w float pointer.
         static Quaternion from_xyzw(const float* xyzw_) {
-            return Quaternion{xyzw_[0], xyzw_[1], xyzw_[2], xyzw_[3]};
+            return Quaternion::from_xyzw(xyzw_[0], xyzw_[1], xyzw_[2], xyzw_[3]);
         }
 
         /// Construct Quaternion from w/x/y/z float pointer.
         static Quaternion from_wxyz(const float* wxyz_) {
-            return Quaternion{wxyz_[1], wxyz_[2], wxyz_[3], wxyz_[0]};
+            return Quaternion::from_xyzw(wxyz_[1], wxyz_[2], wxyz_[3], wxyz_[0]);
         }
 
         float x() const {

rerun_cpp/tests/archetypes/transform3d.cpp

@@ -79,7 +79,7 @@ SCENARIO(
     }
 
     SECTION("TranslationRotationScale") {
-        const auto rotation = rrd::Quaternion{1.0f, 2.0f, 3.0f, 4.0f};
+        const auto rotation = rrd::Quaternion::from_xyzw(1.0f, 2.0f, 3.0f, 4.0f);
 
         Transform3D manual;
         rrd::TranslationRotationScale3D translation_rotation_scale;