The MSVC CRT library is not overrideable by other build systems

[ChrisDenton]

For -windows-msvc targets linking the C runtime (e.g. C main, etc) is done in the libc crate which then hard codes the CRT startup libraries to use, which means they can't be overridden (without hacks or no_std) except to choose between dynamic or static linking. This makes it difficult to select the right CRT for certain builds. This matters particularly when integrating Rust alongside existing C/C++ build systems. The same CRT must be used in all cases.

I would propose that rustc should behave more like cl (the MSVC compiler) in this case. We should use /DEFAULTLIB: to link the CRT so the library is overridable rather than hard coded. This also means it can work with existing tools rather than needing anything custom for rustc.

[spangaer]

It looks like you figured this out yourself?
#39016 (comment)

Though I've noticed it doesn't seem to work with 1.79, but does with 1.83
#39016 (comment)

[ChrisDenton]

Yes, this is an area I've been trying to improve. I made changes to CRT linking so it's now possible. I'll close this issue as completed.

However, it's not quite perfect. There's no way for other tools to know when CRT has been overridden, which they will need to know in order to build compatible C/C++ libraries.