-Wmicrosoft: Don't warn on non-inline pure virtual method definitions

MSVC and clang with -fms-extensions allow pure virtual methods to be
defined inline after the "= 0" tokens.  Clang warns on these because it
is not standard, but incorrectly warns on out-of-line definitions, which
are standard.

With this change, clang will only warn on inline definitions of pure
virtual methods.

Fixes some self-host warnings on out-of-line definitions of pure virtual
destructors.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@192244 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index ba1822c..52297d7 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -9633,7 +9633,7 @@
 
     // MSVC permits the use of pure specifier (=0) on function definition,
     // defined at class scope, warn about this non standard construct.
-    if (getLangOpts().MicrosoftExt && FD->isPure())
+    if (getLangOpts().MicrosoftExt && FD->isPure() && FD->isCanonicalDecl())
       Diag(FD->getLocation(), diag::warn_pure_function_definition);
 
     if (!FD->isInvalidDecl()) {