Describe valid argument domain for 8-bit wide locales to prevent common error

calling ctype functions with signed char as an argument.

lib/libc/locale/isalnum.3

@@ -54,6 +54,8 @@ function tests for any character for which
 or
 .Xr isdigit 3
 is true.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isalpha.3

@@ -54,6 +54,8 @@ function tests for any character for which
 or
 .Xr islower 3
 is true.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isascii.3

@@ -49,6 +49,8 @@ function tests for an
 .Tn ASCII
 character, which is any character with a value less than or
 equal to octal 0177.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 .Sh SEE ALSO
 .Xr ctype 3 ,
 .Xr ascii 7

lib/libc/locale/isblank.3

@@ -46,6 +46,8 @@
 The
 .Fn isblank
 function tests for a space or tab character.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 .Sh RETURN VALUES
 The
 .Fn isblank

lib/libc/locale/iscntrl.3

@@ -50,6 +50,8 @@
 The
 .Fn iscntrl
 function tests for any control character.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isdigit.3

@@ -50,6 +50,8 @@
 The
 .Fn isdigit
 function tests for any decimal-digit character.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isgraph.3

@@ -50,6 +50,8 @@
 The
 .Fn isgraph
 function tests for any printing character except space.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/islower.3

@@ -50,6 +50,8 @@
 The
 .Fn islower
 function tests for any lower-case letters.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isprint.3

@@ -50,6 +50,8 @@
 The
 .Fn isprint
 function tests for any printing character including space (' ').
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/ispunct.3

@@ -53,6 +53,8 @@ function tests for any printing character except for space (' ') or a
 character for which
 .Xr isalnum 3
 is true.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isspace.3

@@ -50,6 +50,8 @@
 The
 .Fn isspace
 function tests for the standard white-space characters.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isupper.3

@@ -50,6 +50,8 @@
 The
 .Fn isupper
 function tests for any upper-case letter.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/isxdigit.3

@@ -50,6 +50,8 @@
 The
 .Fn isxdigit
 function tests for any hexadecimal-digit character.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 In the ASCII character set, this includes the following characters
 (with their numeric values shown in octal):
 .Pp

lib/libc/locale/tolower.3

@@ -51,6 +51,8 @@ The
 .Fn tolower
 function converts an upper-case letter to the corresponding lower-case
 letter.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 .Sh RETURN VALUES
 If the argument is an upper-case letter, the
 .Fn tolower

lib/libc/locale/toupper.3

@@ -51,6 +51,8 @@ The
 .Fn toupper
 function converts a lower-case letter to the corresponding 
 upper-case letter.
+For 8-bit wide locales the value of the argument is
+representable as an unsigned char or the value of EOF.
 .SH RETURN VALUES
 If the argument is a lower-case letter, the
 .Fn toupper