Use C99/stdint.h types over non-portable (deprecated) glibc types
Bug: https://bugs.gentoo.org/715840

--- a/lib/mpi_type.h
+++ b/lib/mpi_type.h
@@ -26,6 +26,7 @@
 #ifndef MPI_TYPE_H
 #define MPI_TYPE_H
 
+#include <stdint.h>
 
 /*******************************************************************************
  * Define MPI_POINTER if it hasn't already been defined. By default MPI_POINTER
@@ -50,7 +51,7 @@
 
 
 typedef int32_t   S32;
-typedef u_int32_t U32;
+typedef uint32_t U32;
 
 typedef struct _S64
 {