indent(1): respect SIMPLE_BACKUP_SUFFIX environment variable

[kevans]

Summary

Address a personal nit: indent(1) defaults to using ".BAK" as the suffix
for backup files. This is the most inconvenient part of some of my workflow, so
allow it to be made consistent with the SIMPLE_BACKUP_SUFFIX environment variable.

Test Plan

Ensure tests still pass and that the default suffix remains ".BAK" and
that it can be overridden properly.

[cem]

I assume this matches some existing convention (re: name of the environment variable)?

[kevans]

Indeed, the name of the env variable follows convention established by GNU indent(1) and, perhaps more importantly, our patch(1) also uses it if specified unless overridden by a flag.

[pstef]

usr.bin/indent/indent.c

104

I'd suggest const char *envval = NULL;

[kevans]

• Const'ify envval based on suggestion by pstef@

[kevans]

Ping @emaste =)

[emaste]

Approved.