Replace blas/f2c with clean C++ implementations

libeigen/eigen!2402

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>

blas/lsame.cpp

@@ -0,0 +1,15 @@
+// This file is part of Eigen, a lightweight C++ template library
+// for linear algebra.
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <cctype>
+
+#include "blas.h"
+
+// LSAME returns true if ca and cb are the same letter, regardless of case.
+extern "C" EIGEN_BLAS_API int lsame_(const char *ca, const char *cb) {
+  return std::toupper(static_cast<unsigned char>(*ca)) == std::toupper(static_cast<unsigned char>(*cb));
+}