RFR: 8245098: Make SafeFetch32/N available earlier

[Per Liden]

We have a need for SafeFetch32 during initializing of ZGC (see [1]). 
However, the SafeFetch32/N stubs are currently generated too late, in 
the stubRoutines_init2() phase, which is after the GC has been 
initialized. I propose we move the initialization of these stubs to the 
stubRoutines_init1() phase, which is before the GC has been initialized, 
to make them available during GC initialization.

Please note that this patch touches platforms I can't easily test 
(x86-32, arm, ppc, s390). If you have access to one of those machines, I 
would appreciate if you could do some light verification.

Bug: https://bugs.openjdk.java.net/browse/JDK-8245098
Webrev: http://cr.openjdk.java.net/~pliden/8245098/webrev.0
Testing: Tier1-3 on all Oracle supported platforms.

/Per

[1] https://bugs.openjdk.java.net/browse/JDK-8245106