Fix for G++.
Fix for G++.

Avoids this error:
../src/muz_qe/heap_trie.h: In member function ‘virtual unsigned int heap_trie<Key, KeyLE, Value>::leaf::num_leaves() const’:
../src/muz_qe/heap_trie.h:91:64: error: there are no arguments to ‘ref_count’ that depend on a template parameter, so a declaration of ‘ref_count’ must be available [-fpermissive]
../src/muz_qe/heap_trie.h:91:64: note: (if you use ‘-fpermissive’, G++ will accept your code, but allowing the use of an undeclared name is deprecated)

Signed-off-by: Christoph M. Wintersteiger <df906fa73c281118b7012d85069f1a6194ecf7a3@microsoft.com>

melted/z3,mschlaipfer/z3,kyledewey/z3,gmeer/z3,traiansf/z3-java,smilliken/z3,jslhs/z3,syjzwjj/z3,traiansf/z3-java,jslhs/z3,Drup/z3,felixdae/z3,conceptofproof/z3,seahorn/z3,traiansf/z3-java,zardus/z3,leodemoura/z3,Baha/z3,smilliken/z3,huangshiyou/z3,syjzwjj/z3,zardus/z3,jslhs/z3,375670450/z3,seahorn/z3,zhuyue1314/z3,conceptofproof/z3,Drup/z3,Drup/z3,jirislaby/z3,jslhs/z3,gmeer/z3,Baha/z3,375670450/z3,gmeer/z3,jslhs/z3,hguenther/z3,smilliken/z3,belyaev-mikhail/z3,huangshiyou/z3,zhuyue1314/z3,mschlaipfer/z3,mschlaipfer/z3,375670450/z3,leodemoura/z3,mschlaipfer/z3,Baha/z3,belyaev-mikhail/z3,jirislaby/z3,syjzwjj/z3,Baha/z3,huangshiyou/z3,zhuyue1314/z3,belyaev-mikhail/z3,375670450/z3,leodemoura/z3,375670450/z3,felixdae/z3,melted/z3,jirislaby/z3,melted/z3,zardus/z3,leodemoura/z3,zardus/z3,Drup/z3,syjzwjj/z3,wujunzero/z3,huangshiyou/z3,jslhs/z3,belyaev-mikhail/z3,Baha/z3,conceptofproof/z3,traiansf/z3-java,zhuyue1314/z3,kyledewey/z3,hguenther/z3,zardus/z3,mschlaipfer/z3,felixdae/z3,melted/z3,huangshiyou/z3,traiansf/z3-java,leodemoura/z3,smilliken/z3,hguenther/z3,gmeer/z3,seahorn/z3,traiansf/z3-java,kyledewey/z3,felixdae/z3,wujunzero/z3,syjzwjj/z3,syjzwjj/z3,hguenther/z3,conceptofproof/z3,gmeer/z3,wujunzero/z3,wujunzero/z3,Drup/z3,zardus/z3,wujunzero/z3,belyaev-mikhail/z3,hguenther/z3,leodemoura/z3,zhuyue1314/z3,zhuyue1314/z3,seahorn/z3,smilliken/z3,jirislaby/z3,melted/z3,kyledewey/z3,kyledewey/z3,conceptofproof/z3,375670450/z3,smilliken/z3,Drup/z3,gmeer/z3,conceptofproof/z3,seahorn/z3,jirislaby/z3,huangshiyou/z3,seahorn/z3,belyaev-mikhail/z3,felixdae/z3,Baha/z3,melted/z3,hguenther/z3,felixdae/z3,jirislaby/z3,wujunzero/z3,kyledewey/z3,mschlaipfer/z3