RFR: 8297417: Poly1305IntrinsicFuzzTest fails with tag mismatch exception [v2]

[Volodymyr Paprotski]

> From https://github.com/openjdk/jdk/pull/10582, `t0` gets clobbered if `rscratch` is used. Example, [here](https://github.com/openjdk/jdk/blob/09f70dad2fe3f0691afacded6c38f61fa8a0d28d/src/hotspot/cpu/x86/stubGenerator_x86_64_poly.cpp#L605-L606): 
> 
> 
>   __ mov(t0, a0);
>   __ andq(t0, ExternalAddress(poly1305_mask44()), rscratch); // First limb (R^4[43:0])

Volodymyr Paprotski has updated the pull request incrementally with one additional commit since the last revision:

  remove rscratch from top regmap and ForceUnreachable test

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/11308/files
  - new: https://git.openjdk.org/jdk/pull/11308/files/aa8cea41..a2c8907f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11308&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11308&range=00-01

  Stats: 24 lines in 2 files changed: 0 ins; 2 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/11308.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11308/head:pull/11308

PR: https://git.openjdk.org/jdk/pull/11308