Bug 1743020 - Part 1: Opt third-party paths out of NoExplicitMoveConstructor checker, r=andi

The function2 library uses an explicit move constructor internally,
which would trigger this checker, and cause a build failure.

Differential Revision: https://phabricator.services.mozilla.com/D145689

build/clang-plugin/NoExplicitMoveConstructorChecker.cpp

@@ -8,7 +8,9 @@
 void NoExplicitMoveConstructorChecker::registerMatchers(
     MatchFinder *AstMatcher) {
   AstMatcher->addMatcher(
-      cxxConstructorDecl(isExplicitMoveConstructor()).bind("node"), this);
+      cxxConstructorDecl(isExplicitMoveConstructor(), isFirstParty())
+          .bind("node"),
+      this);
 }
 
 void NoExplicitMoveConstructorChecker::check(