Enable basic support for riscv64

[Hamlin-Li]

Hi,
Can you take a look at this patch which try to bring basic riscv64 support to zstd-jni?
This patch is based on pr #281 , and pr #280 .

Thanks!

Test

I have run the test via QEMU by following command:

CC=riscv64-linux-gnu-gcc ./sbt -java-home ~/jdk/build/linux-riscv64-server-release/images/jdk/ testOnly

There are lots of output, seems there is no error, and the bottom lines of output are:

[info] Total number of tests run: 151
[info] Suites: completed 3, aborted 0
[info] Tests: succeeded 151, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.

[luben]

LGTM, I just want to verify if I have the right cross compiler toolchain.

[codecov-commenter]

Codecov Report

Merging #282 (fb2faf0) into master (780994b) will increase coverage by 0.14%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

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@@             Coverage Diff              @@
##             master     #282      +/-   ##
============================================
+ Coverage     59.60%   59.74%   +0.14%     
  Complexity      301      301              
============================================
  Files            26       26              
  Lines          1421     1421              
  Branches        164      164              
============================================
+ Hits            847      849       +2     
+ Misses          419      417       -2     
  Partials        155      155              

[Hamlin-Li]

Thanks for your review!