Correct unit Makefile to use OBJ rather than LIBS

Previously the order of the libraries in LIB would effect whether the
unit tests compiled.

Use OBJ rather than LIBS to ensure the --start-group/--end-group flags are
used in linking.

Previously, if a file in CProver changed, though the libraries would be
rebuilt, the unit tests wouldn't be relinked against the new library,
meaning you would get out of date binaries.

This change ensures that the link process is rerun if any of the
libraries are rebuilt.

Adding dependency to cprover libs for other unit executables

Author: thk123

unit/Makefile

@@ -15,19 +15,21 @@ include ../src/common
 cprover.dir:
 	$(MAKE) $(MAKEARGS) -C ../src
 
-LIBS += ../src/ansi-c/ansi-c$(LIBEXT) \
-        ../src/cpp/cpp$(LIBEXT) \
-        ../src/json/json$(LIBEXT) \
-        ../src/linking/linking$(LIBEXT) \
-        ../src/util/util$(LIBEXT) \
-        ../src/big-int/big-int$(LIBEXT) \
-        ../src/goto-programs/goto-programs$(LIBEXT) \
-        ../src/pointer-analysis/pointer-analysis$(LIBEXT) \
-        ../src/langapi/langapi$(LIBEXT) \
-        ../src/assembler/assembler$(LIBEXT) \
-        ../src/analyses/analyses$(LIBEXT) \
-        ../src/solvers/solvers$(LIBEXT) \
-        # Empty last line
+CPROVER_LIBS =../src/ansi-c/ansi-c$(LIBEXT) \
+              ../src/cpp/cpp$(LIBEXT) \
+              ../src/json/json$(LIBEXT) \
+              ../src/linking/linking$(LIBEXT) \
+              ../src/util/util$(LIBEXT) \
+              ../src/big-int/big-int$(LIBEXT) \
+              ../src/goto-programs/goto-programs$(LIBEXT) \
+              ../src/pointer-analysis/pointer-analysis$(LIBEXT) \
+              ../src/langapi/langapi$(LIBEXT) \
+              ../src/assembler/assembler$(LIBEXT) \
+              ../src/analyses/analyses$(LIBEXT) \
+              ../src/solvers/solvers$(LIBEXT) \
+              # Empty last line
+
+OBJ += $(CPROVER_LIBS)
 
 TESTS = unit_tests$(EXEEXT) \
         miniBDD$(EXEEXT) \
@@ -49,11 +51,11 @@ test: all
 unit_tests$(EXEEXT): $(OBJ)
 	$(LINKBIN)
 
-miniBDD$(EXEEXT): miniBDD$(OBJEXT)
+miniBDD$(EXEEXT): miniBDD$(OBJEXT) $(CPROVER_LIBS)
 	$(LINKBIN)
 
-string_utils$(EXEEXT): string_utils$(OBJEXT)
+string_utils$(EXEEXT): string_utils$(OBJEXT) $(CPROVER_LIBS)
 	$(LINKBIN)
 
-sharing_node$(EXEEXT): sharing_node$(OBJEXT)
+sharing_node$(EXEEXT): sharing_node$(OBJEXT) $(CPROVER_LIBS)
 	$(LINKBIN)