Mark up "unsigned char".

lib/libc/string/memccpy.3

@@ -50,7 +50,9 @@ to string
 .Fa dst .
 If the character
 .Fa c
-(as converted to an unsigned char) occurs in the string
+(as converted to an
+.Vt "unsigned char" )
+occurs in the string
 .Fa src ,
 the copy stops and a pointer to the byte after the copy of
 .Fa c

lib/libc/string/memchr.3

@@ -52,7 +52,8 @@ The
 function
 locates the first occurrence of
 .Fa c
-(converted to an unsigned char)
+(converted to an
+.Vt "unsigned char" )
 in string
 .Fa b .
 .Pp

lib/libc/string/memcmp.3

@@ -61,7 +61,9 @@ The
 function
 returns zero if the two strings are identical,
 otherwise returns the difference between the first two differing bytes
-(treated as unsigned char values, so that
+(treated as
+.Vt "unsigned char"
+values, so that
 .Sq Li \e200
 is greater than
 .Sq Li \&\e0 ,

lib/libc/string/memset.3

@@ -52,7 +52,9 @@ writes
 .Fa len
 bytes of value
 .Fa c
-(converted to an unsigned char) to the string
+(converted to an
+.Vt "unsigned char" )
+to the string
 .Fa b .
 .Sh RETURN VALUES
 The