Fix static plugin CI linkage

Author: SineStriker

.github/workflows/ci.yml

@@ -214,4 +214,6 @@ jobs:
 
       - name: Test
         shell: msys2 {0}
-        run: ctest --test-dir build --output-on-failure --no-tests=error
+        run: |
+          export PATH="$(cygpath -u "$RUNNER_TEMP")/stdcorelib/bin:$PATH"
+          ctest --test-dir build --output-on-failure --no-tests=error

include/stdcorelib/plugin/plugin.h

@@ -66,7 +66,11 @@ namespace stdc::plugin {
 
 }
 
-#if !defined(STDC_PLUGIN_LIBRARY)
+#if !defined(STDC_PLUGIN_LIBRARY) && defined(_MSC_VER)
+// MSVC needs the dllimport declaration when inline registry code references the
+// exported _head and _tail data members. GNU-family compilers must instantiate
+// AddFactory locally because an outer explicit instantiation does not instantiate
+// the nested class.
 extern template class STDC_PLUGIN_EXPORT stdc::StaticRegistry<stdc::plugin::StaticPlugin>;
 #endif