RFR: 8293098: GHA: Harmonize GCC version handling for host and cross builds

[Aleksey Shipilev]

Caught this headache while trying to bump to Ubuntu 22.04, which required touching way too many surprising places. 

Current GHA scripts define `apt-gcc-version` a bit weirdly: host and cross builds version differ in carrying the "gcc-major-version" inside of it. That is, "host" builds do `apt-gcc-version: '10=10.3.0-1ubuntu1~20.04'`, while cross builds do `apt-gcc-version: default: '10.3.0-1ubuntu1~20.04'`

I propose we harmonize these to simplify GCC updates: split out the `gcc-major-version` for host builds, and pull the versions from cross builds into `main`, where all other versions belong. Additionally, this handles the x86_32 case that requires "-multilib" package, which is currently hacked through the "version" string.

Additional testing:
 - [ ] GHA

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

Commit messages:
 - Trying to handle x86_32 again
 - Pull the cross-version from defaults
 - Fix

Changes: https://git.openjdk.org/jdk/pull/10083/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10083&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293098
  Stats: 34 lines in 3 files changed: 18 ins; 3 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/10083.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10083/head:pull/10083

PR: https://git.openjdk.org/jdk/pull/10083