Sema: honour dllexport in itanium more faithfully

Although the itanium environment uses the itanium layout for C++, treat the
dllexport semantics more similarly to the MSVC specification.  This preserves
the existing behaviour for the use of the itanium ABI on non-windows-itanium
environments.  Export the inline definitions too.

llvm-svn: 284288
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index b04bad2..93e626f 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -5546,7 +5546,8 @@
 
       if (MD->isInlined()) {
         // MinGW does not import or export inline methods.
-        if (!Context.getTargetInfo().getCXXABI().isMicrosoft())
+        if (!Context.getTargetInfo().getCXXABI().isMicrosoft() &&
+            !Context.getTargetInfo().getTriple().isWindowsItaniumEnvironment())
           continue;
 
         // MSVC versions before 2015 don't export the move assignment operators