RFR: JDK-8302801: Remove fdlibm C sources

[Joe Darcy]

While the review of https://github.com/openjdk/jdk/pull/12800 finishes up, I thought I'd get out for the review the next phase of the FDLIBM port: removing the FDLIBM C sources from the repo.

A repo with the changes for JDK-8302027 and this PR successful build on the default set of platform and successfully run tier 1 tests, which includes tests of the math library.

There are a few remaining references to the case-independent string "fdlibm" in the make directory and HotSpot sources. HotSpot contains a partial fork for FDLIBM (a tine of FDLIBM?) to use for intrinsics. The remaining make machinery contains logic to determine what set of gcc options can be used for the compile.

The intention of this change is to remove use of FDLIBM for the core libraries.

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Depends on: https://git.openjdk.org/jdk/pull/12800

Commit messages:
 - JDK-8302801: Remove fdlibm C sources

Changes: https://git.openjdk.org/jdk/pull/12821/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12821&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302801
  Stats: 6609 lines in 63 files changed: 0 ins; 6609 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12821.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12821/head:pull/12821

PR: https://git.openjdk.org/jdk/pull/12821