fix XFAIL conditions for what.pass.cpp

Author: abhina-sree

libcxx/test/std/thread/futures/futures.future_error/what.pass.cpp

@@ -13,6 +13,10 @@
 //
 // XFAIL: stdlib=apple-libc++ && target={{.+}}-apple-macosx10.{{9|10|11}}
 
+// VC Runtime's std::exception::what() method is not marked as noexcept, so
+// this fails.
+// XFAIL: target={{.+}}-windows-msvc && !libcpp-no-vcruntime
+
 // <future>
 //
 // class future_error