Linux: Remove unused code from standard C++ libraries with use_static_cpp=yes (reduces binary size by 1.3mb!)

[dsnopek]

When building the test project on Linux with scons use_static_cpp=yes (which is the default!) this will generate a binary that is ~1.3mb smaller!

Platform / Compiler	Size Before	Size After	Change
Linux / GCC 13	2,866 KB	1,548 KB	-1,318 KB (-46.0%)
Linux / Clang 18	3,063 KB	1,247 KB	-1,816 KB (-59.3%)

I've done a bunch of experimenting and investigation on Windows, and I don't think there's a similar gain to be had there. We don't support the use_static_cpp=yes option on any other platforms (only Linux and Windows)

I've made the same changes in CMake as well, and they seem to work in my testing

[Ivorforce]

I thought there was some problem with use_static_cpp (compat depending on who builds it), but it seems like upstream Godot also does use it for linux.

I can't really judge the build flags; I'm not familiar with them. If the buildsystem team doesn't review I can give a yolo approval in a few days

[dsnopek]

I thought there was some problem with use_static_cpp (compat depending on who builds it), but it seems like upstream Godot also does use it for linux.

use_static_cpp can actually help solve compatibility problems: it allows your extension to work on other Linux distros with incompatible versions of the standard C++ libraries (by statically linking them, rather than using the dynamic library from the system)