minisat: Only define __STDC_XXX_MACROS if not already defined.

minisat: Only define __STDC_XXX_MACROS if not already defined.

Replace;
 #define __STDC_LIMIT_MACROS
 #define __STDC_FORMAT_MACROS

With
 #ifndef __STDC_LIMIT_MACROS
 #define __STDC_LIMIT_MACROS
 #endif
 #ifndef __STDC_FORMAT_MACROS
 #define __STDC_FORMAT_MACROS
 #endif

This fixes a compile warning if you are defining these macros in your
CXXFLAGS (as some distros do).