nss: disable MSVC

Fails with
../../coreconf/rules.mk:164: *** multiple target patterns.  Stop.
make[2]: *** [../coreconf/rules.mk:44: bltest] Error 2
make[1]: *** [coreconf/rules.mk:44: cmd] Error 2
make: *** [manifest.mn:26: prepare_build] Error 2

And even the existing recipe fails with
make[3]: *** No rule to make target '../certhigh/WINNT10.0-22621_x86_64_64_OPT.OBJ/certhtml.obj', needed by 'WINNT3.4.5.x86_64_x86_64_64_OPT.OBJ/nss3.dll'.  Stop.
on MSVC 193 for me.

recipes/nss/all/conanfile.py

@@ -64,7 +64,10 @@ def validate(self):
             raise ConanInvalidConfiguration("Macos ARM64 builds not yet supported. Contributions are welcome.")
         if Version(self.version) < "3.74":
             if self.settings.compiler == "clang" and Version(self.settings.compiler.version) >= 13:
-                raise ConanInvalidConfiguration("nss < 3.74 requires clang < 13 .")
+                raise ConanInvalidConfiguration("nss < 3.74 requires clang < 13.")
+        if is_msvc(self):
+            # https://c3i.jfrog.io/c3i/misc/summary.html?json=https://c3i.jfrog.io/c3i/misc/logs/pr/19262/4-windows-visual_studio/nss/3.89/summary.json
+            raise ConanInvalidConfiguration("MSVC is currently not supported. Contributions are welcome.")
 
     def build_requirements(self):
         if self._settings_build.os == "Windows":