RFR: 8308975: Fix signed integer overflow in compiler code, part 2 [v2]

[Dean Long]

> This is a followup from part 1.  I had to use java_add/subtract/multiply/negate in a few more places.
> cpu_loads_process had an overflow on BSD when the first snapshot is relative to the epoch in 1970.
> Use unsigned for C2 Type hash functions.

Dean Long has updated the pull request incrementally with two additional commits since the last revision:

 - use uint64_t for nanos
 - fix alignment

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14188/files
  - new: https://git.openjdk.org/jdk/pull/14188/files/41b13dc8..a50b4f01

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14188&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14188&range=00-01

  Stats: 22 lines in 2 files changed: 4 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/14188.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14188/head:pull/14188

PR: https://git.openjdk.org/jdk/pull/14188