Small changes to compile on Mac.

Makefile

@@ -63,7 +63,11 @@ endif
 
 endif
 
-LIBS := -ldl -lrt
+# LIBS := -ldl -lrt
+LIBS := -ldl
+ifneq ($(findstring Darwin, $(shell uname)), Darwin)
+   LIBS += -lrt
+endif
 
 ifneq ($(READLINE),0)
 CFLAGS += -DABC_USE_READLINE

src/misc/util/abc_global.h

@@ -272,7 +272,7 @@ static inline int      Abc_Lit2LitL( int * pMap, int Lit )    { return Abc_LitNo
 typedef ABC_INT64_T abctime;
 static inline abctime Abc_Clock()
 {
-#if defined(LIN) || defined(LIN64)
+#if defined(LIN) || defined(LIN64) && !(__APPLE__ & __MACH__)
     struct timespec ts;
     if ( clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts) < 0 ) 
         return (abctime)-1;