RFR: 8254744: Clean-up CodeBlob::align_code_offset

[Claes Redestad]

- Modernize by using align_up
- Move definition of the trivial CodeHeap::header_size() to header to help inlining, which optimizes align_code_offset
  and others. No big gain, but we're calling CodeHeap::header_size() 1300+ times on Hello World, and when inlined it's
  just a constant fold.

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Commit messages:
 - Merge branch 'master' into align_code
 - Clean-up align_code_offset

Changes: https://git.openjdk.java.net/jdk/pull/651/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=651&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254744
  Stats: 9 lines in 3 files changed: 0 ins; 6 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/651.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/651/head:pull/651

PR: https://git.openjdk.java.net/jdk/pull/651