RFR: 8287195: AArch64: Client VM build failure after JDK-8283689

[Nick Gasson]

The client build fails because foreignGlobals_aarch64.cpp uses Matcher without `#ifdef COMPILER2`.  However there's a latent bug here on SVE machines where `RegSpiller::pd_reg_size()` returns the SVE register size but other code that uses the register spill area (e.g. `DowncallStubGenerator::generate()` and `AArch64Architecture.VECTOR_REG_SIZE`) assume that we always save 16 bytes.  Since we don't support any calling conventions where arguments/results are passed in long vectors we should
just save the first 128 bits of the register, like x86 does.

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Commit messages:
 - 8287195: AArch64: Client VM build failure after JDK-8283689

Changes: https://git.openjdk.java.net/jdk/pull/8908/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8908&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287195
  Stats: 18 lines in 1 file changed: 0 ins; 15 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8908.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8908/head:pull/8908

PR: https://git.openjdk.java.net/jdk/pull/8908