include Makefile.common before using $(BuildMode) to get its definition


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68167 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/unittests/Makefile.unittest b/unittests/Makefile.unittest
index 5832d6a..1c75e44 100644
--- a/unittests/Makefile.unittest
+++ b/unittests/Makefile.unittest
@@ -14,11 +14,10 @@
 # Set up variables for building a unit test.
 ifdef TESTNAME
 
-LLVMUnitTestDir := $(LLVM_OBJ_ROOT)/$(BuildMode)/unittests
-LLVMUnitTestExe := $(LLVMUnitTestDir)/$(TESTNAME)Tests$(EXEEXT)
-
 include $(LEVEL)/Makefile.common
 
+LLVMUnitTestExe = $(BuildMode)/$(TESTNAME)Tests$(EXEEXT)
+
 CPP.Flags += -I$(LLVM_SRC_ROOT)/utils/unittest/googletest/include/
 CPP.Flags += -Wno-variadic-macros
 LIBS += -lGoogleTest -lUnitTestMain