Enable building LLVMgold.dll under mingw.

Summary:
Plugins can (and should) be enabled under mingw if we are building
libLLVM.dll, so this is just a missed case. This allows LLVMgold.dll to
be built now under mingw.

Reviewers: llvm-commits, pirama, beanz, chapuni

Reviewed By: chapuni

Subscribers: chapuni, mgorny

Differential Revision: https://reviews.llvm.org/D37116

llvm-svn: 311973
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index a2ab128..8680614 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -792,7 +792,7 @@
 # Plugin support
 # FIXME: Make this configurable.
 if(WIN32 OR CYGWIN)
-  if(BUILD_SHARED_LIBS)
+  if(BUILD_SHARED_LIBS OR LLVM_BUILD_LLVM_DYLIB)
     set(LLVM_ENABLE_PLUGINS ON)
   else()
     set(LLVM_ENABLE_PLUGINS OFF)