erlc warnings are sent to stdout instead of to stderr

[eksperimental]

Describe the bug
erlc warnings are sent to stdout instead of to stderr.

To Reproduce

$ cat src/has_warning.erl
-module(has_warning).
my_fn() -> ok.

$ erlc "src/has_warning.erl" > stdout.txt 2> stderr.txt

$ cat stderr.txt

$ cat stdout.txt
src/has_warning.erl:2:1: Warning: function my_fn/0 is unused
%    2| my_fn() -> ok.
%     | ^

Expected behavior
To have warnings sent to stderr.

Affected versions
OTP 27 and previous ones.