[riscv-port-jdk17u:riscv-port] RFR: 8295926: RISC-V: C1: Fix LIRGenerator::do_LibmIntrinsic

[Dingli Zhang]

Please review this backport to riscv-port-jdk17u.
Backport of [JDK-8295926](https://bugs.openjdk.org/browse/JDK-8295926). Applies cleanly.
Case test/hotspot/jtreg/compiler/floatingpoint/TestLibmIntrinsics.java failed before this patch.

Testing:
- test/hotspot/jtreg/compiler/floatingpoint/TestLibmIntrinsics.java passed on qemu and unmatched.
- Tier1 passed without new failure on unmacthed (release).

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Commit messages:
 - 8295926: RISC-V: C1: Fix LIRGenerator::do_LibmIntrinsic

Changes: https://git.openjdk.org/riscv-port-jdk17u/pull/10/files
 Webrev: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=10&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295926
  Stats: 100 lines in 2 files changed: 95 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/10.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/10/head:pull/10

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/10