Fix Wshorten-64-to-32 warning in gemm parallelizer

Eigen/src/Core/products/Parallelizer.h

diff --git a/Eigen/src/Core/products/Parallelizer.h b/Eigen/src/Core/products/Parallelizer.h
index c3172aa..59335af 100644
--- a/Eigen/src/Core/products/Parallelizer.h
+++ b/Eigen/src/Core/products/Parallelizer.h
@@ -178,7 +178,7 @@
   pb_max_threads = std::max<Index>(1, std::min<Index>(pb_max_threads, static_cast<Index>( work / kMinTaskSize ) ));
 
   // compute the number of threads we are going to use
-  int threads = std::min<int>(nbThreads(), pb_max_threads);
+  int threads = std::min<int>(nbThreads(), static_cast<int>(pb_max_threads));
 
   // if multi-threading is explicitly disabled, not useful, or if we already are
   // inside a parallel session, then abort multi-threading