Fix cygwin problems

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/util/debug.cpp

@@ -10,6 +10,7 @@ Author: Leonardo de Moura
 #include <set>
 #include <string>
 #include <memory>
+#include <cstdlib>
 
 #ifndef _WINDOWS
 // Support for pid

src/util/exception.cpp

@@ -17,7 +17,7 @@ exception::exception(std::string const & msg):m_msg(msg) {
 exception::exception(exception const & e):m_msg(e.m_msg) {
 }
 
-exception::~exception() {
+exception::~exception() noexcept {
 }
 
 char const * exception::what() const noexcept {

src/util/exception.h

@@ -16,7 +16,7 @@ public:
     exception(char const * msg);
     exception(std::string const & msg);
     exception(exception const & ex);
-    virtual ~exception();
+    virtual ~exception() noexcept;
     virtual char const * what() const noexcept;
 };