RFR(XXS): 8057780: Fix ppc build after "8050147: StoreLoad barrier interferes with stack usages"

[Volker Simonis]

Hi,

could somebody please review and sponsor the following tiny fixes in
os_linux_ppc.cpp/os_aix_ppc.cpp:

http://cr.openjdk.java.net/~simonis/webrevs/8057780/
https://bugs.openjdk.java.net/browse/JDK-8057780

They simply fix a typo on Linux/PPC64 and an incorrect method
signature on AIX which have been introduced by "8050147: StoreLoad
barrier interferes with stack usages"

Thank you and best regards,
Volker