Only include misc_testsuite/winch when testing Winch (#6905)

This commit optimizes the use of CI resources by avoiding unnecessary
duplication of WebAssembly spec tests when using the Cranelift compiler
strategy. Previously, Cranelift was tested against both the official spec test
suite and Winch's test suite, the latter being a subset of the former. This
commit eliminates this redundancy.

build.rs

@@ -36,7 +36,13 @@ fn main() -> anyhow::Result<()> {
             test_directory_module(out, "tests/misc_testsuite/memory64", strategy)?;
             test_directory_module(out, "tests/misc_testsuite/component-model", strategy)?;
             test_directory_module(out, "tests/misc_testsuite/function-references", strategy)?;
-            test_directory_module(out, "tests/misc_testsuite/winch", strategy)?;
+            // The testsuite of Winch is a subset of the official
+            // WebAssembly test suite, until parity is reached. This
+            // check is in place to prevent Cranelift from duplicating
+            // tests.
+            if *strategy == "Winch" {
+                test_directory_module(out, "tests/misc_testsuite/winch", strategy)?;
+            }
             Ok(())
         })?;