RFR: 8305618: Move gcold out of tier1 [v2]

[Leo Korinth]

> 8305618: Move gcold out of tier1
> 
> Remove gcold out from tier1. Related to [JDK-8298981](https://bugs.openjdk.org/browse/JDK-8298981). Moving gcbasher out of tier1 was more controversial, and will be done later --- if at all.

Leo Korinth has updated the pull request incrementally with two additional commits since the last revision:

 - move gc groups near each others
 - As suggested by Shipilëv, move to tier3

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13340/files
  - new: https://git.openjdk.org/jdk/pull/13340/files/72805395..8a6b6262

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13340&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13340&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/13340.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13340/head:pull/13340

PR: https://git.openjdk.org/jdk/pull/13340