ulimit(3): Improve UL_{GET,SET}FSIZE wording

[obiwac]

Summary

Reword the UL_GETFSIZE and UL_SETFSIZE descriptions to say 512-byte
blocks and make the setter's argument clearer.

While here, improve mdoc markup and pull in other small improvements.

MFC after: 3 days
Obtained from: https://github.com/apple-oss-distributions/libc
Sponsored by: Klara, Inc.

Test Plan

Rendered manpage:

	ULIMIT(3)               FreeBSD Library Functions Manual               ULIMIT(3)

	NAME
     	  ulimit – get and set process limits

	LIBRARY
     	  Standard C Library (libc, -lc)

	SYNOPSIS
     	  #include <ulimit.h>

     	  long
     	  ulimit(int cmd, ...);

	DESCRIPTION
     	  The ulimit() function will get and set process limits.  Currently, this is
     	  limited to the maximum file size.  The cmd argument is one of the
     	  following:

     	  UL_GETFSIZE  will return the maximum file size of the current process, in
                  	units of 512-byte blocks.

     	  UL_SETFSIZE  will attempt to set the maximum file size of the current
                  	process and its children, using the second argument (expressed
                  	as a long).

	RETURN VALUES
     	  Upon successful completion, ulimit() returns the value requested;
     	  otherwise, the value -1 is returned and the global variable errno is set to
     	  indicate the error.

	ERRORS
     	  The ulimit() function will fail if:

     	  [EINVAL]           The command specified was invalid.

     	  [EPERM]            The limit specified to ulimit() would have raised the
                        	maximum limit value, and the caller is not the super-
                        	user.

	SEE ALSO
     	  getrlimit(2)

	STANDARDS
     	  The ulimit() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

	HISTORY
     	  The ulimit() function first appeared in FreeBSD 5.0.

	BUGS
     	  The ulimit() function provides limited precision for setting and retrieving
     	  process limits.  If there is a need for greater precision than the type
     	  long provides, the getrlimit(2) and setrlimit(2) functions should be
     	  considered.

	FreeBSD 16.0-CURRENT             October 7, 2026                       ULIMIT(3)

[des]

lib/libc/gen/ulimit.3

55–56

[obiwac]

replace error description with -std

[obiwac]

lib/libc/gen/ulimit.3

55–56

TIL