Fix compilation of Readline on mingw.org's MinGW

readline/ChangeLog
2019-12-23  Eli Zaretskii  <eliz@gnu.org>

	* posixstat.h (S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH)
	(S_IXOTH, S_IRWXG, S_IRWXO): Define if undefined, even if S_IRWXU
	is defined, because non-Posix systems may defined only the user
	bits.

readline/readline/CHANGELOG

@@ -1,3 +1,10 @@
+2019-12-23  Eli Zaretskii  <eliz@gnu.org>
+
+	* posixstat.h (S_IRGRP, S_IWGRP, S_IXGRP, S_IROTH, S_IWOTH)
+	(S_IXOTH, S_IRWXG, S_IRWXO): Define if undefined, even if S_IRWXU
+	is defined, because non-Posix systems may defined only the user
+	bits.
+
 [Readline-specific changelog.  Descriptions of changes to the source are
  found in the bash changelog.]
 

readline/readline/posixstat.h

@@ -132,6 +132,26 @@
 #  define S_IRWXU	(S_IRUSR | S_IWUSR | S_IXUSR)
 #  define S_IRWXG	(S_IRGRP | S_IWGRP | S_IXGRP)
 #  define S_IRWXO	(S_IROTH | S_IWOTH | S_IXOTH)
+#else  /* !S_IRWXU */
+   /* S_IRWXU is defined, but "group" and "other" bits might not be
+      (happens in certain versions of MinGW).  */
+#  if !defined (S_IRGRP)
+#    define S_IRGRP	(S_IREAD  >> 3)		/* read, group */
+#    define S_IWGRP	(S_IWRITE >> 3)		/* write, group */
+#    define S_IXGRP	(S_IEXEC  >> 3)		/* execute, group */
+#  endif /* !S_IRGRP */
+
+#  if !defined (S_IROTH)
+#    define S_IROTH	(S_IREAD  >> 6)		/* read, other */
+#    define S_IWOTH	(S_IWRITE >> 6)		/* write, other */
+#    define S_IXOTH	(S_IEXEC  >> 6)		/* execute, other */
+#  endif /* !S_IROTH */
+#  if !defined (S_IRWXG)
+#    define S_IRWXG	(S_IRGRP | S_IWGRP | S_IXGRP)
+#  endif
+#  if !defined (S_IRWXO)
+#    define S_IRWXO	(S_IROTH | S_IWOTH | S_IXOTH)
+#  endif
 #endif /* !S_IRWXU */
 
 /* These are non-standard, but are used in builtins.c$symbolic_umask() */