Only enable MinGW-w64 pow() workaround if needed

src/assembler.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 1385 matching lines @@
     m *= m;
     if ((n & 2) != 0) p *= m;
     m *= m;
     n >>= 2;
   }
   return p;
 }
 
 
 double power_double_double(double x, double y) {
-#ifdef __MINGW64_VERSION_MAJOR
+#if defined(__MINGW64_VERSION_MAJOR) && (!defined(__MINGW64_VERSION_RC) || __MINGW64_VERSION_RC < 1)
   // MinGW64 has a custom implementation for pow.  This handles certain
   // special cases that are different.
   if ((x == 0.0 || isinf(x)) && isfinite(y)) {
     double f;
     if (modf(y, &f) != 0.0) return ((x == 0.0) ^ (y > 0)) ? V8_INFINITY : 0;
   }
 
   if (x == 2.0) {
     int y_int = static_cast<int>(y);
     if (y == y_int) return ldexp(1.0, y_int);
@@ skipping 140 matching lines @@
     assembler_->RecordRelocInfo(RelocInfo::POSITION, state_.current_position);
     state_.written_position = state_.current_position;
     written = true;
   }
 
   // Return whether something was written.
   return written;
 }
 
 } }  // namespace v8::internal