RFR: 8241503: C2: Share MacroAssembler between mach nodes during code emission

[Cesar Soares]

Hi there, can I please get some reviews on this change? The patch is to make the code reuse the same C2_MacroAssembler object during the emission of CPU instructions of a given compilation.

As you'll see the change affects all backends. I've done my best to keep the changes minimal/simple.

I tested this locally on Linux x86_64, x86_32 and MacOS Arm32, and ARM64.

**I need help testing the changes on PPC, S390, and RISCV**. I cross-compiled the JVM locally and the builds are all succeeding, but I couldn't use an emulator (yet) or any real hardware (no access to one) to test the changes on these platforms. I see that GitHub actions do some tests on S390 and PPC but the tests seem to not be extensive.

Thanks in advance,
Cesar

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Commit messages:
 - work
 - work
 - work
 - work
 - work
 - work
 - work
 - work
 - merging
 - merge fix for macos building
 - ... and 11 more: https://git.openjdk.java.net/jdk/compare/239ac2a5...7c739f77

Changes: https://git.openjdk.java.net/jdk/pull/9074/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9074&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8241503
  Stats: 2393 lines in 49 files changed: 117 ins; 332 del; 1944 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9074.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9074/head:pull/9074

PR: https://git.openjdk.java.net/jdk/pull/9074