Use int64_t for KLU_INDEXTYPE if SUNDIALS_INT64_T is true.

`long int` is 32 bits wide on systems that use an LLP64 data model
(e.g., Windows). Use a type for which the C standard guarantees that it
is 64-bit instead (i.e., `int64_t`).

Signed-off-by: Markus Mützel <[email protected]>

src/sunlinsol/klu/sunlinsol_klu.c

@@ -16,6 +16,7 @@
  * the SUNLINSOL package.
  * -----------------------------------------------------------------*/
 
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sundials/sundials_math.h>
@@ -49,7 +50,7 @@
  */
 
 #if defined(SUNDIALS_INT64_T)
-#define KLU_INDEXTYPE long int
+#define KLU_INDEXTYPE int64_t
 #else
 #define KLU_INDEXTYPE int
 #endif