nixpkgs/systems: Add ucrt64 as MinGW libc

The Minimalist Gnu for Windows distribution comes with support for
the traditional msvcrt libc, as well as ucrt64 libc. The latter
being the newer universal compiler runtime. We follow the msys2
environment naming convention[1]:

| name       | toolchain | arch    | libc   | libc++    |
|------------|-----------|---------|--------|-----------|
| mingw32    | gcc       | i686    | msvcrt | libstdc++ |
| mingw64    | gcc       | x86_64  | msvcrt | libstdc++ |
| ucrt64     | gcc       | x86_64  | ucrt   | libstdc++ |
| clang32    | llvm      | i686    | ucrt   | libc++    |
| clang64    | llvm      | x86_64  | ucrt   | libc++    |
| clangarm64 | llvm      | aarch64 | ucrt   | libc++    |

For now nixpkgs only supports the first three with this commit.

--
[1]: https://www.msys2.org/docs/environments/

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/systems/examples.nix b/lib/systems/examples.nix
index 8d9c09561ddb..2a067663f98c 100644
--- a/lib/systems/examples.nix
+++ b/lib/systems/examples.nix
@@ -313,6 +313,11 @@ rec {
     libc = "msvcrt"; # This distinguishes the mingw (non posix) toolchain
   };
 
+  ucrt64 = {
+    config = "x86_64-w64-mingw32";
+    libc = "ucrt"; # This distinguishes the mingw (non posix) toolchain
+  };
+
   # BSDs
 
   x86_64-freebsd = {