getaddrinfo: fix gai_strerror signature

Several platforms declare gai_strerror to return char* rather than
const char*.  Worse, on mingw, if UNICODE is defined, it is defined
to return WCHAR*, which means the result is in unicode but an
application expecting bytes for characters will only see a one-byte
answer.

* m4/getaddrinfo.m4 (gl_GETADDRINFO): Detect broken signatures,
and work around mingw with UNICODE defined.
(gl_PREREQ_GETADDRINFO): Drop redundant decl check.
* m4/netdb_h.m4 (gl_NETDB_H_DEFAULTS): Add witness.
* modules/netdb (Makefile.am): Substitute it.
* lib/netdb.in.h (gai_strerror): Declare replacement.
* lib/gai_strerror.c (rpl_gai_strerror): Fix signature.
* doc/posix-functions/gai_strerror.texi (gai_strerror): Document
the fix.

Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/doc/posix-functions/gai_strerror.texi b/doc/posix-functions/gai_strerror.texi
index ece2bdc991..d94a6ed9bd 100644
--- a/doc/posix-functions/gai_strerror.texi
+++ b/doc/posix-functions/gai_strerror.texi
@@ -10,13 +10,18 @@ Portability problems fixed by Gnulib:
 @itemize
 @item
 This function is missing on some platforms:
-HP-UX 11.11, IRIX 6.5, OSF/1 4.0, Solaris 7, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
+HP-UX 11.11, IRIX 6.5, OSF/1 4.0, Solaris 7, Cygwin 1.5.x, Interix
+3.5, BeOS.
+@item
+This function is only available in @code{<ws2tcpip.h>} on some
+platforms:
+mingw.
+@item
+This function's return type is @code{char *} instead of @code{const char *}
+on some platforms:
+AIX 7.1, HP-UX 11, OSF/1 5.1, Solaris 9, mingw.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
-@item
-This function's return type is @code{char *} instead of @code{const char *}
-on some platforms:
-AIX 7.1, HP-UX 11, OSF/1 5.1, Solaris 9.
 @end itemize