RFR: 8294941: GHA: Cut down cross-compilation sysroots

[Aleksey Shipilev]

In GHA cross-compilation, we don't need everything from the sysroot, because we use native compilers for the compilation. Therefore, we can cut them even deeper and reclaim significant amount of cache space. This would also make cache eviction less likely, which saves time on recreating the sysroots when that happens.

Current sysroots take about 300M per arch, which quickly multiplies up for multiple arches (we build 5 now) users (ballparking at about 200 active contributors). This amounts to about 1500M caches per job, and 300G in caches across our org. 

In my local tests, new aarch64 sysroot tar.gz gets reduced from 315M to just 85M, about 3.7x improvement. Even deeper cuts are possible, but they would affect the redundant `.so`-s in `/usr/lib/${arch}/`. That would be much more fragile to do and might affect our builds. Therefore, I stopped at doing just these.

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/10601/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10601&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294941
  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/10601.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10601/head:pull/10601

PR: https://git.openjdk.org/jdk/pull/10601