[MS ABI]: Fix mangling function arguments for template types to be compatible with MSVC

MS name mangling supports cache for first 10 distinct function
arguments.  The error was when non cached template type occurred twice
(e.g. 11th and 12th).  For such case in code there is another cache
table TemplateArgStrings (for performance reasons).  Then one '@'
character at the end of the mangled name taken from this table was
missing.  For other cases the missing '@' character was added in
the call to mangleSourceName(TemplateMangling) in the cache miss code,
but the cache hit code didn't add it.

This fixes a regression from r362560.

Patch by Adam Folwarczny <adamf88@gmail.com>!

Differential Revision: https://reviews.llvm.org/D68099

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374543 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/MicrosoftMangle.cpp

@@ -846,7 +846,7 @@ void MicrosoftCXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
               TemplateArgStringStorage.save(TemplateMangling.str());
         }
       } else {
-        Out << Found->second; // Outputs a StringRef.
+        Out << Found->second << '@'; // Outputs a StringRef.
       }
     } else {
       Out << Found->second; // Outputs a back reference (an int).

test/CodeGenCXX/mangle-ms-back-references.cpp

@@ -66,3 +66,20 @@ namespace foo {
 void foo() { }
 // CHECK: "?foo@0@YAXXZ"
 }
+
+class T01;
+class T02;
+class T03;
+class T04;
+class T05;
+class T06;
+class T07;
+class T08;
+class T09;
+class T10;
+class T11;
+template <typename T>
+class H;
+
+void ManyParams(T01 &, T02 &, T03 &, T04 &, T05 &, T06 &, T07 &, T08 &, T09 &, T10 &, H<T11> &, H<T11> &) {}
+// CHECK: "?ManyParams@@YAXAAVT01@@AAVT02@@AAVT03@@AAVT04@@AAVT05@@AAVT06@@AAVT07@@AAVT08@@AAVT09@@AAVT10@@AAV?$H@VT11@@@@AAV?$H@VT11@@@@@Z"