posix: c_lib_ext: fnmatch: added Doxygen

Added Doxygen on new functions and on fnmatch function

Signed-off-by: Harun Spago <harun.spago.code@gmail.com>

Author: Spago123

include/zephyr/posix/fnmatch.h

@@ -38,11 +38,11 @@
 
 #define FNM_NOMATCH 1 /**< Match failed */
 
-#define FNM_NOESCAPE	0x01 /* Disable backslash escaping. */
-#define FNM_PATHNAME	0x02 /* Slash must be matched by slash. */
-#define FNM_PERIOD	0x04 /* Period must be matched by period. */
-#define FNM_CASEFOLD	0x08 /* Pattern is matched case-insensitive */
-#define FNM_LEADING_DIR 0x10 /* Ignore /<tail> after Imatch. */
+#define FNM_NOESCAPE    0x01 /**< Disable backslash escaping */
+#define FNM_PATHNAME    0x02 /**< Slash must be matched by slash */
+#define FNM_PERIOD      0x04 /**< Period must be matched by period */
+#define FNM_CASEFOLD    0x08 /**< Pattern is matched case-insensitive */
+#define FNM_LEADING_DIR 0x10 /**< Only match the initial segment of a string up to the first '/' */
 
 #ifdef __cplusplus
 extern "C" {