Make testcase myrandom() noinline.

With clang 13 none/tests/amd64/amd64locked fails because of what
looks like a clang optimization error. do_bt_G_E_tests is the
point of failure, and one factor is that clang 13 is inlining
myrandom().

none/tests/amd64/amd64locked.c

@@ -14,6 +14,8 @@ typedef  unsigned short          UShort;
 typedef  unsigned long           UWord;
 typedef  char                    HChar;
 
+
+__attribute__((noinline))
 unsigned myrandom(void)
 {
    /* Simple multiply-with-carry random generator. */