RFR: 8255975: Fix AArch64 OpenJDK build failure with gcc-5

[Hao Sun]

As one C++17 feature, the argument 'message' of static_assert can be optional.
This feature, i.e. static_assert with no message, is supported by gcc-6 or
higher.[1]

Add 'message' arguments in order to avoid compilation failures if gcc-5 is used.

[1] https://gcc.gnu.org/projects/cxx-status.html

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Commit messages:
 - 8255975: Fix AArch64 OpenJDK build failure with gcc-5

Changes: https://git.openjdk.java.net/jdk/pull/1088/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1088&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255975
  Stats: 15 lines in 1 file changed: 0 ins; 0 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1088.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1088/head:pull/1088

PR: https://git.openjdk.java.net/jdk/pull/1088