system_data_types.7: Document regmatch_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

@@ -82,6 +82,25 @@ and
 .I ssize_t
 types in this page.
 .TP
+.I regmatch_t
+.IP
+Include:
+.IR <regex.h> .
+.IP
+.EX
+typedef struct {
+    regoff_t    rm_so; /* Byte offset from start of string
+                        * to start of substring */
+    regoff_t    rm_eo; /* Byte offset from start of string of the
+                        * first character after the end of substring */
+} regmatch_t;
+.EE
+.IP
+Conforming to: POSIX.1-2001 and later.
+.IP
+See also:
+.BR regexec (3)
+.TP
 .I regoff_t
 .IP
 Include:
@@ -104,8 +123,8 @@ type or a
 type.
 .IP
 See also the
-.\".I regmatch_t	FIXME
-.\"structure and the
+.I regmatch_t
+structure and the
 .I ptrdiff_t
 and
 .I ssize_t