Enabling xtensor-blas with xeus-cpp-lite (#252)

We have been using xtensor-blas with xeus-cpp-lite through a patch on
emscripten-forge

emscripten-forge/recipes#2318

This PR upstreams the necessary patch. We use the f2c based openblas
build (providing libopenblas.so) on emscripten-forge to run
xtensor-blas.

---------

Co-authored-by: Johan Mabille <[email protected]>

Author: anutosh491

include/xtensor-blas/xblas_config.hpp

@@ -30,6 +30,10 @@
 #include "xtensor-blas/xblas_config_cling.hpp"
 #endif
 
+#if defined(__CLANG_REPL__) && defined(__EMSCRIPTEN__)
+#include "xtensor-blas/xblas_config_cling.hpp"
+#endif
+
 namespace xt
 {
     using blas_index_t = BLAS_IDX;

include/xtensor-blas/xblas_config_cling.hpp.in

@@ -10,17 +10,28 @@
 #ifndef XBLAS_CONFIG_CLING_HPP
 #define XBLAS_CONFIG_CLING_HPP
 
-#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR_64@)
-#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR_32@)
-#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR@)
-
 #ifndef XTENSOR_USE_FLENS_BLAS
 
 #define HAVE_CBLAS 1
 
+#if defined(__CLING__)
+
+#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR_64@)
+#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR_32@)
+#pragma cling add_library_path(@XTENSOR_BLAS_CLING_LIBRARY_DIR@)
 #pragma cling load("libblas")
 #pragma cling load("liblapack")
 
-#endif
+#elif defined(__EMSCRIPTEN__) && defined(__CLANG_REPL__)
+
+#include <clang/Interpreter/CppInterOp.h>
+static bool _openblas_loaded = []() {
+    Cpp::LoadLibrary(@OPENBLAS_CPPINTEROP_LIBRARY_PATH@, false);
+    return true;
+}();
 
 #endif
+
+#endif // XTENSOR_USE_FLENS_BLAS
+
+#endif // XBLAS_CONFIG_CLING_HPP