system_data_types.7: Add 'regex_t'

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man7/system_data_types.7

@@ -786,6 +786,29 @@ and
 .I ssize_t
 types in this page.
 .RE
+.\"------------------------------------- regex_t ----------------------/
+.TP
+.I regex_t
+.RS
+Include:
+.IR <regex.h> .
+.PP
+.EX
+typedef struct {
+    size_t  re_nsub; /* Number of parenthesized subexpressions. */
+} regex_t;
+.EE
+.PP
+This is a structure type used in regular expression matching.
+It holds a compiled regular expression, compiled with
+.IR regcomp (3).
+.PP
+Conforming to:
+POSIX.1-2001 and later.
+.PP
+See also:
+.BR regex (3)
+.RE
 .\"------------------------------------- regmatch_t -------------------/
 .TP
 .I regmatch_t