Link against libopenblas.lib on Windows

Without a respective lib, linking would inevitably fail.  We also add
a check for cblas.h, and if either is not found, disable ext/tensor
with a respective warning.

See also <RubixML#22>.

Author: cmb69

ext/config.w32

@@ -1,20 +1,26 @@
 ARG_ENABLE("tensor", "enable tensor", "no");
 
 if (PHP_TENSOR != "no") {
-  EXTENSION("tensor", "tensor.c", null, "-I"+configure_module_dirname);
-  ADD_SOURCES(configure_module_dirname + "/kernel", "main.c memory.c exception.c debug.c backtrace.c object.c array.c string.c fcall.c require.c file.c operators.c math.c concat.c variables.c filter.c iterator.c exit.c time.c", "tensor");
-  /* PCRE is always included on WIN32 */
-  AC_DEFINE("ZEPHIR_USE_PHP_PCRE", 1, "Whether PHP pcre extension is present at compile time");
-  if (PHP_JSON != "no") {
-    ADD_EXTENSION_DEP("tensor", "json");
-    AC_DEFINE("ZEPHIR_USE_PHP_JSON", 1, "Whether PHP json extension is present at compile time");
+  if (CHECK_LIB("libopenblas.lib", "tensor", PHP_TENSOR) &&
+      CHECK_HEADER_ADD_INCLUDE("cblas.h", "CFLAGS_TENSOR")
+  ) {
+    EXTENSION("tensor", "tensor.c", null, "-I"+configure_module_dirname);
+    ADD_SOURCES(configure_module_dirname + "/kernel", "main.c memory.c exception.c debug.c backtrace.c object.c array.c string.c fcall.c require.c file.c operators.c math.c concat.c variables.c filter.c iterator.c exit.c time.c", "tensor");
+    /* PCRE is always included on WIN32 */
+    AC_DEFINE("ZEPHIR_USE_PHP_PCRE", 1, "Whether PHP pcre extension is present at compile time");
+    if (PHP_JSON != "no") {
+      ADD_EXTENSION_DEP("tensor", "json");
+      AC_DEFINE("ZEPHIR_USE_PHP_JSON", 1, "Whether PHP json extension is present at compile time");
+    }
+    ADD_SOURCES(configure_module_dirname + "/include", "arithmetic.c comparison.c linear_algebra.c signal_processing.c settings.c", "tensor");
+    ADD_SOURCES(configure_module_dirname + "/tensor", "algebraic.zep.c arithmetic.zep.c arraylike.zep.c comparable.zep.c special.zep.c statistical.zep.c trigonometric.zep.c tensor.zep.c vector.zep.c columnvector.zep.c matrix.zep.c settings.zep.c", "tensor");
+    ADD_SOURCES(configure_module_dirname + "/tensor/exceptions", "tensorexception.zep.c invalidargumentexception.zep.c dimensionalitymismatch.zep.c runtimeexception.zep.c", "tensor");
+    ADD_SOURCES(configure_module_dirname + "/tensor/decompositions", "cholesky.zep.c eigen.zep.c lu.zep.c svd.zep.c", "tensor");
+    ADD_SOURCES(configure_module_dirname + "/tensor/reductions", "ref.zep.c rref.zep.c", "tensor");
+    ADD_FLAG("CFLAGS_TENSOR", "/D ZEPHIR_RELEASE /Oi /Ot /Oy /Ob2 /Gs /GF /Gy /GL");
+    ADD_FLAG("CFLAGS", "/D ZEPHIR_RELEASE /Oi /Ot /Oy /Ob2 /Gs /GF /Gy /GL");
+    ADD_FLAG("LDFLAGS", "/LTCG");
+  } else {
+    WARNING("tensor not enabled; libraries and headers not found");
   }
-  ADD_SOURCES(configure_module_dirname + "/include", "arithmetic.c comparison.c linear_algebra.c signal_processing.c settings.c", "tensor");
-  ADD_SOURCES(configure_module_dirname + "/tensor", "algebraic.zep.c arithmetic.zep.c arraylike.zep.c comparable.zep.c special.zep.c statistical.zep.c trigonometric.zep.c tensor.zep.c vector.zep.c columnvector.zep.c matrix.zep.c settings.zep.c", "tensor");
-	ADD_SOURCES(configure_module_dirname + "/tensor/exceptions", "tensorexception.zep.c invalidargumentexception.zep.c dimensionalitymismatch.zep.c runtimeexception.zep.c", "tensor");
-	ADD_SOURCES(configure_module_dirname + "/tensor/decompositions", "cholesky.zep.c eigen.zep.c lu.zep.c svd.zep.c", "tensor");
-	ADD_SOURCES(configure_module_dirname + "/tensor/reductions", "ref.zep.c rref.zep.c", "tensor");
-  ADD_FLAG("CFLAGS_TENSOR", "/D ZEPHIR_RELEASE /Oi /Ot /Oy /Ob2 /Gs /GF /Gy /GL");
-  ADD_FLAG("CFLAGS", "/D ZEPHIR_RELEASE /Oi /Ot /Oy /Ob2 /Gs /GF /Gy /GL");
-  ADD_FLAG("LDFLAGS", "/LTCG");
 }