See https://groups.google.com/forum/#!topic/minisat/FCocZsC8oMQ
This seems to only be a problem with newer versions of g++, and
upstream development seems to have stopped in 2013.

diff -rupN minisat-2.2.0/core/SolverTypes.h minisat-2.2.0.patched/core/SolverTypes.h
--- a/minisat/core/SolverTypes.h	2010-07-10 17:07:36.000000000 +0100
+++ b/minisat/core/SolverTypes.h	2014-03-29 11:57:49.000000000 +0000
@@ -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 = false);

     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; }
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