POSIX msgfmt and escape sequences in msgid and msgid_plural strings

[Bruno Haible]

https://posix.rhansen.org/p/gettext_draft
Line 1031

"C-language escape sequences in message strings shall be processed as
specified for character string literals in the ISO C standard ..."

Issue: The way this is written, it is not possible to write, in a dot-po file:
msgid "Program terminated.\n"

Suggestion:
This sentence should be extended to hold for *all* string literals in a
dot-po file. So that C escape sequences can be used in particular
in message_identifier (line 901) and untranslated_string_plural (line 902).

Both GNU msgfmt and Solaris msgfmt do it like this.