RFR: 8283626: AArch64: Set relocInfo::offset_unit to 4 [v2]

[Evgeny Astigeevich]

> AArch64 instructions size is 4 bytes. Two lowest bits of `relocInfo` offsets can be discarded.
> Tested with release and fastdebug builds:
> - `gtest`: Passed.
> - `tier1`...`tier4`: Passed

Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:

  Updated code comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7991/files
  - new: https://git.openjdk.java.net/jdk/pull/7991/files/1104f4e4..9b040c31

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7991&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7991&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7991.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7991/head:pull/7991

PR: https://git.openjdk.java.net/jdk/pull/7991