RFR: 8319705: RISC-V: signumF/D intrinsics fails compiler/intrinsics/math/TestSignumIntrinsic.java

[Hamlin Li]

Hi,
Can you review the patch to fix the bug introduced by [JDK-8317971](https://bugs.openjdk.org/browse/JDK-8317971) which implemented signumF/D intrinsics.
But seems the intrinsics failed since day 1 (I checkouted the commit to verify it.)
Thanks

## Test
hotspot tests:

test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java
test/hotspot/jtreg/compiler/c2/PolynomialRoot.java


other jdk tests contains Math.signum(...):

test/jdk/java/math/BigInteger/BigIntegerTest.java 
test/jdk/java/math/BigInteger/largeMemory/DivisionOverflow.java
test/jdk/java/math/BigInteger/SerializationTests.java
test/jdk/java/math/BigInteger/ModInvTime.java
test/jdk/java/math/BigDecimal/SquareRootTests.java
test/jdk/java/math/BigDecimal/DivideTests.java
test/jdk/java/lang/Math/IeeeRecommendedTests.java
test/jdk/java/lang/Math/IeeeRemainderTests.java

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

Commit messages:
 - Kill cr
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/16557/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16557&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8319705
  Stats: 26 lines in 3 files changed: 2 ins; 8 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/16557.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16557/head:pull/16557

PR: https://git.openjdk.org/jdk/pull/16557