[Chapel Merge] Add env var overrides for recent memory settings

Branch: refs/heads/main
Revision: 715bc67
Author: ronawho
Log Message:

Merge pull request #18396 from ronawho/env-var-override-mem-configs

Add env var overrides for recent memory settings

[reviewed by @gbtitus]

Add CHPL_RT_INTERLEAVE_MEMORY to control memory interleaving at
runtime and CHPL_RT_MERGE_SPLIT_CHUNKS to control whether jemalloc is
allowed to merge and split chunks. These are undocumented since they
aren't meant to be user-facing, they're just here in case we need to
experiment in the field.

Modified Files:
M runtime/src/mem/jemalloc/mem-jemalloc.c

Compare: https://github.com/chapel-lang/chapel/compare/eff355a7f869...715bc67ff0f7