Create Makefile target unity_test

Summary: unity_test will compile db_test with unity.a instead of librocksdb.a. This will test both the compilation and some small amount of runtime.

Test Plan: This is a test :)

Reviewers: kradhakrishnan

Reviewed By: kradhakrishnan

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D48297

Makefile

@@ -602,6 +602,11 @@ unity.a: unity.o
 	$(AM_V_AR)rm -f $@
 	$(AM_V_at)$(AR) $(ARFLAGS) $@ unity.o
 
+# try compiling db_test with unity
+unity_test: db/db_test.o util/db_test_util.o $(TESTHARNESS) unity.a
+	$(AM_LINK)
+	./unity_test
+
 rocksdb.h rocksdb.cc: build_tools/amalgamate.py Makefile $(LIB_SOURCES) unity.cc
 	build_tools/amalgamate.py -I. -i./include unity.cc -x include/rocksdb/c.h -H rocksdb.h -o rocksdb.cc
 

build_tools/rocksdb-lego-determinator

@@ -219,7 +219,7 @@ UNITY_COMMANDS="[
             $CLEANUP_ENV,
             {
                 'name':'Build, test unity test',
-                'shell':'$SHM $DEBUG V=1 make J=1 unity',
+                'shell':'$SHM $DEBUG V=1 make J=1 unity_test',
                 'user':'root'
             },
         ],
@@ -227,8 +227,6 @@ UNITY_COMMANDS="[
     }
 ]"
 
-UNITY_COMMANDS=$DISABLE_COMMANDS
-
 #
 # Build RocksDB lite
 #