ci: re-enable build job for x86_64-pc-cygwin (#832)

Author: briansmith

.github/workflows/build.yml

@@ -95,9 +95,7 @@ jobs:
           x86_64-unknown-dragonfly,
           x86_64-unknown-haiku,
           x86_64-unknown-linux-none,
-          # TODO: once libc support for cygwin is released
-          # https://github.com/rust-lang/libc/pull/4308
-          # x86_64-pc-cygwin,
+          x86_64-pc-cygwin,
         ]
     steps:
       - uses: actions/checkout@v6