unittests/JITTests: Don't use --export-dynamic but --export-all-symbols on cygming.

GNU ld/PECOFF accepts but ignores them below;
  --version-script
  --export-dynamic
  --rpath

FIXME: autoconf should be aware of them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120179 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/CMakeLists.txt b/unittests/CMakeLists.txt
index 41e20cf..7953fac 100644
--- a/unittests/CMakeLists.txt
+++ b/unittests/CMakeLists.txt
@@ -82,6 +82,10 @@
 
 add_llvm_unittest(JIT ${JITTestsSources})
 
+if(MINGW)
+  set_property(TARGET JITTests PROPERTY LINK_FLAGS -Wl,--export-all-symbols)
+endif()
+
 add_llvm_unittest(Transforms
   Transforms/Utils/Cloning.cpp
   )