[COFF] Avoid forward declaring StringSet, fix build

This should fix the build after SVN r316178, which worked fine
on GCC 5.4, but failed on clang with errors like these:

MinGW.h:26:3: error: too few template arguments for class template 'StringSet'
  StringSet<> ExcludeSymbols;
  ^
lld/Common/LLVM.h:28:30: note: template is declared here
  template<typename T> class StringSet;

Don't forward declare and add the using directive in the main
lld/Common/LLVM.h header, but just qualify the class name
in MinGW.h instead.

1 files changed, 0 insertions, 2 deletions

diff --git a/lld/include/lld/Common/LLVM.h b/lld/include/lld/Common/LLVM.h
index 582abfb339f..b5d0e2bffb0 100644
--- a/lld/include/lld/Common/LLVM.h
+++ b/lld/include/lld/Common/LLVM.h
@@ -25,7 +25,6 @@ namespace llvm {
   // ADT's.
   class Error;
   class StringRef;
-  template<typename T> class StringSet;
   class Twine;
   class MemoryBuffer;
   class MemoryBufferRef;
@@ -58,7 +57,6 @@ namespace lld {
   // ADT's.
   using llvm::Error;
   using llvm::StringRef;
-  using llvm::StringSet;
   using llvm::Twine;
   using llvm::MemoryBuffer;
   using llvm::MemoryBufferRef;