[newlib-cygwin/main] Correct isspace(3) man page (copied wording from isalpha(3))

[Jeff Johnston]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=c2ccfae99752ce1f52806efd1b06bbb2cc60b849

commit c2ccfae99752ce1f52806efd1b06bbb2cc60b849
Author: Keith Thompson <Keith.S.Thompson@gmail.com>
Date:   Thu Aug 13 17:13:50 2026 -0400

    Correct isspace(3) man page (copied wording from isalpha(3))

Diff:
---
 newlib/libc/ctype/isspace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/newlib/libc/ctype/isspace.c b/newlib/libc/ctype/isspace.c
index 0def2c0ce..784f4d7ae 100644
--- a/newlib/libc/ctype/isspace.c
+++ b/newlib/libc/ctype/isspace.c
@@ -18,7 +18,8 @@ SYNOPSIS
 DESCRIPTION
 <<isspace>> is a macro which classifies singlebyte charset values by table
 lookup.  It is a predicate returning non-zero for whitespace
-characters, and 0 for other characters.  It is defined only when <<isascii>>(<[c]>) is true or <[c]> is EOF.
+characters, and 0 for other characters.  It is defined only if
+<[c]> is representable as an unsigned char or if <[c]> is EOF.
 
 <<isspace_l>> is like <<isspace>> but performs the check based on the
 locale specified by the locale object locale.  If <[locale]> is