Changes and fixed suggested by Clifford Wolf.

Makefile

@@ -122,6 +122,10 @@ ifneq ($(findstring Darwin, $(shell uname)), Darwin)
    LIBS += -lrt
 endif
 
+ifdef ABC_USE_LIBSTDCXX
+   LIBS += -lstdc++
+   $(info $(MSG_PREFIX)Using explicit -lstdc++)
+endif
 
 $(info $(MSG_PREFIX)Using CFLAGS=$(CFLAGS))
 CXXFLAGS += $(CFLAGS)

src/sat/bsat2/SolverTypes.h

@@ -47,7 +47,7 @@ struct Lit {
     int     x;
 
     // Use this as a constructor:
-    friend Lit mkLit(Var var, bool sign = false);
+    friend Lit mkLit(Var var, bool sign);
 
     bool operator == (Lit p) const { return x == p.x; }
     bool operator != (Lit p) const { return x != p.x; }
@@ -55,7 +55,7 @@ struct Lit {
 };
 
 
-inline  Lit  mkLit     (Var var, bool sign) { Lit p; p.x = var + var + (int)sign; return p; }
+inline  Lit  mkLit     (Var var, bool sign = false) { Lit p; p.x = var + var + (int)sign; return p; }
 inline  Lit  operator ~(Lit p)              { Lit q; q.x = p.x ^ 1; return q; }
 inline  Lit  operator ^(Lit p, bool b)      { Lit q; q.x = p.x ^ (unsigned int)b; return q; }
 inline  bool sign      (Lit p)              { return p.x & 1; }

src/sat/glucose/SolverTypes.h

@@ -55,14 +55,14 @@ struct Lit {
     int     x;
 
     // Use this as a constructor:
-    friend Lit mkLit(Var var, bool sign = false);
+    friend Lit mkLit(Var var, bool sign);
     bool operator == (Lit p) const { return x == p.x; }
     bool operator != (Lit p) const { return x != p.x; }
     bool operator <  (Lit p) const { return x < p.x;  } // '<' makes p, ~p adjacent in the ordering.
 };
 
 
-inline  Lit  mkLit     (Var var, bool sign) { Lit p; p.x = var + var + (int)sign; return p; }
+inline  Lit  mkLit     (Var var, bool sign = false) { Lit p; p.x = var + var + (int)sign; return p; }
 inline  Lit  operator ~(Lit p)              { Lit q; q.x = p.x ^ 1; return q; }
 inline  Lit  operator ^(Lit p, bool b)      { Lit q; q.x = p.x ^ (unsigned int)b; return q; }
 inline  bool sign      (Lit p)              { return p.x & 1; }