Fix ASAN/TSAN/UBSAN/MSAN CI

Author: JMazurkiewicz

libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.nttp.pass.cpp

@@ -53,7 +53,9 @@ struct MaybeNoexceptNegation {
 };
 
 template <bool IsNoexcept>
-MaybeNoexceptNegation<IsNoexcept> maybe_noexcept_negation() noexcept; // not defined
+MaybeNoexceptNegation<IsNoexcept> maybe_noexcept_negation() noexcept {
+  return {};
+}
 
 constexpr void basic_tests() {
   { // Test constant functions