Detect compiling from Linux gnu to Linux musl as cross compiling (#2010)

For maturin to correctly use bundled sysconfig Python when compiling from Linux gnu host to Linux musl target, we need to detect it as cross compiling, otherwise it will only find Python interpreters on the host that was compiled for glibc.

src/cross_compile.rs

@@ -27,16 +27,9 @@ pub fn is_cross_compiling(target: &Target) -> Result<bool> {
         // Not cross-compiling to compile for 32-bit Python from windows 64-bit
         return Ok(false);
     }
-
-    if let Some(target_without_env) = target_triple
-        .rfind('-')
-        .map(|index| &target_triple[0..index])
-    {
-        if host.starts_with(target_without_env) {
-            // Not cross-compiling if arch-vendor-os is all the same
-            // e.g. x86_64-unknown-linux-musl on x86_64-unknown-linux-gnu host
-            return Ok(false);
-        }
+    if target_triple.ends_with("windows-gnu") && host.ends_with("windows-msvc") {
+        // Not cross-compiling to compile for Windows GNU from Windows MSVC host
+        return Ok(false);
     }
 
     Ok(true)