Defect in XSH asctime

[Geoff Clare <yyy@xxxxxxxxxxxxx>]

@ page 123 line 4514-4515 section asctime objection [gwc asctime threadsafe]

Problem:

Defect code :  1. Error

The asctime page states:

    The asctime() function need not be reentrant. A function that is
    not required to be reentrant is not required to be thread-safe.

A similar statement appears on other pages for functions that are in
the list of non-thread-safe functions in section 2.9.1 Thread-Safety.

The second sentence was added between SUSv2 and SUSv3.  Unfortunately
it is exactly backwards.  There are many functions that are not
required to be reentrant, but are required to be thread-safe.
For example, printf().

Action:

Replace lines 4514-4515 with:

    The asctime() function need not be thread-safe.  A function that
    is not required to be thread-safe is not required to be reentrant.

Make an equivalent change on all the other pages in XSH that have a
similar statement.