git: openjdk/jdk-sandbox: riscv-port-branch: HotSpotAgent: Only support Linux for riscv64 cpu for now

[duke]

Changeset: 8e6414f3
Author:    Fei Yang <felix.yang at huawei.com>
Date:      2021-05-13 12:07:23 +0000
URL:       https://git.openjdk.java.net/jdk-sandbox/commit/8e6414f33837808205d9db7dac85a21e1b2aaea8

HotSpotAgent: Only support Linux for riscv64 cpu for now

Affected tests:
test/hotspot/jtreg/serviceability/sa/TestJmapCore.java
test/hotspot/jtreg/serviceability/sa/ClhsdbCDSCore.java
test/hotspot/jtreg/serviceability/sa/TestJmapCoreMetaspace.java

Co-authored-by: Zhuxuan Ni <nizhuxuan at huawei.com>

! src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/HotSpotAgent.java