RFR: 8204331: AArch64: fix CAS not embedded in normal graph error.

[Zhongwei Yao]

Hi,

Bug:
https://bugs.openjdk.java.net/browse/JDK-8204331

Webrev:
http://cr.openjdk.java.net/~zyao/8204331/webrev.00/

This patch fixes an assertion error on aarch64 in several jtreg tests. 

The failure assertion is in needs_acquiring_load_exclusive() in aarch64.ad when checking whether the graph is in "leading_to_normal"  shape. The abnormal shape is generated in  LibraryCallKit::inline_unsafe_load_store(). This patch fixes it by swap the order of "Pin SCMProj node" and "Insert post barrier" in LibraryCallKit::inline_unsafe_load_store().

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Best regards,
Zhongwei