test/params_conversion_test.c: fix the use of strtoumax and strtoimax on VMS

We do this by making them aliases for strtoull and strtoll, since long
long is the current largest integer that have this sort of routine on
VMS.
Reviewed-by: NPaul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15366)

test/params_conversion_test.c

@@ -19,6 +19,11 @@
 #  define strcasecmp _stricmp
 # endif
 
+# ifdef OPENSSL_SYS_VMS
+#  define strtoumax strtoull
+#  define strtoimax strtoll
+# endif
+
 typedef struct {
     OSSL_PARAM *param;
     int32_t i32;