RFR: 8357086: os::xxx functions returning memory size should return size_t [v11]

[Anton Artemov]

> Hi,
> 
> in this PR the output value type for functions which return memory are changed, namely:
> 
> 
> static julong available_memory(); --> static MemRes available_memory();
> static julong used_memory(); --> static MemRes used_memory();
> static julong free_memory(); --> static MemRes free_memory(); 
> static jlong total_swap_space(); --> static MemRes total_swap_space();
> static jlong free_swap_space(); --> static MemRes free_swap_space(); 
> static julong physical_memory(); --> static MemRes physical_memory(); 
> 
> 
> `MemRes` is a struct containing a pair of values, `size_t val` to carry the return value, `int err` to carry the error if any. Currently, in case of error the latter is set to -1.
> 
> The changes are done so that the other parts of the code have minimal impact. 
> Tested in GHA and Tiers 1-4.

Anton Artemov has updated the pull request incrementally with one additional commit since the last revision:

  8357086: Added default val to constructor of MemRes.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25450/files
  - new: https://git.openjdk.org/jdk/pull/25450/files/ebf21bce..12055345

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25450&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25450&range=09-10

  Stats: 25 lines in 6 files changed: 0 ins; 0 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/25450.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25450/head:pull/25450

PR: https://git.openjdk.org/jdk/pull/25450