RFR(XS): 8204345: [s390]: no precompiled headers build broken

[Doerr, Martin]

Hi,

the nop() function which calls z_nop() is misplaced in the current implementation which leads to build errors (after JDK-8204195<https://bugs.openjdk.java.net/browse/JDK-8204195>) when not using precompiled headers.

Please review this fix proposal:
http://cr.openjdk.java.net/~mdoerr/8204345_s390_nopch/webrev.00/

Best regards,
Martin