Carla: fix MSVC compatibility

plugins/carlabase/carla.cpp

@@ -333,8 +333,14 @@ void CarlaInstrument::play(sampleFrame* workingBuffer)
     fTimeInfo.bbt.ticksPerBeat   = ticksPerBeat;
     fTimeInfo.bbt.beatsPerMinute = s->getTempo();
 
+#ifndef _MSC_VER
     float buf1[bufsize];
     float buf2[bufsize];
+#else
+    float *buf1 = static_cast<float *>(_alloca(bufsize * sizeof(float)));
+    float *buf2 = static_cast<float *>(_alloca(bufsize * sizeof(float)));
+#endif
+
     float* rBuf[] = { buf1, buf2 };
     std::memset(buf1, 0, sizeof(float)*bufsize);
     std::memset(buf2, 0, sizeof(float)*bufsize);