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.
llvm-svn: 120179
diff --git a/llvm/unittests/Makefile.unittest b/llvm/unittests/Makefile.unittest
index 9a75b2c..8be6174 100644
--- a/llvm/unittests/Makefile.unittest
+++ b/llvm/unittests/Makefile.unittest
@@ -35,9 +35,11 @@
 TESTLIBS = -lGoogleTest -lUnitTestMain
 
 ifeq ($(ENABLE_SHARED), 1)
-  # Add the absolute path to the dynamic library.  This is ok because
-  # we'll never install unittests.
-  LD.Flags += $(RPATH) -Wl,$(SharedLibDir)
+  ifneq (,$(RPATH))
+    # Add the absolute path to the dynamic library.  This is ok because
+    # we'll never install unittests.
+    LD.Flags += $(RPATH) -Wl,$(SharedLibDir)
+  endif
   # Also set {DYLD,LD}_LIBRARY_PATH because OSX ignores the rpath most
   # of the time.
   Run.Shared := $(SHLIBPATH_VAR)="$(SharedLibDir)$${$(SHLIBPATH_VAR):+:}$$$(SHLIBPATH_VAR)"