[gdb/build] Fix typo sys/sockets.h -> sys/socket.h

I'm running into a build breaker:
...
src/gdb/ser-tcp.c:65:13: error: conflicting declaration ‘typedef int
socklen_t’
   65 | typedef int socklen_t;
      |             ^~~~~~~~~
In file included from ../gnulib/import/unistd.h:40,
                 from
/home/vries/gdb_versions/devel/src/gdb/../gnulib/import/pathmax.h:42,
                 from
/home/vries/gdb_versions/devel/src/gdb/../gdbsupport/common-defs.h:120,
                 from src/gdb/defs.h:28,
                 from src/gdb/ser-tcp.c:20:
/usr/include/unistd.h:277:21: note: previous declaration as ‘typedef
__socklen_t socklen_t’
  277 | typedef __socklen_t socklen_t;
      |                     ^~~~~~~~~
...
after commit 05a6b8c28b "Don't unnecessarily redefine 'socklen_t' type in
MinGW builds".

The root cause is a typo in gdb/configure.ac, using sys/sockets.h where
sys/socket.h was meant:
...
AC_CHECK_HEADERS([sys/sockets.h])
...

Fix the typo.

Build and tested on x86_64-linux.

gdb/ChangeLog:

2020-07-27  Tom de Vries  <tdevries@suse.de>

	* configure.ac: Fix sys/sockets.h -> sys/socket.h typo.
	* config.in: Regenerate.
	* configure: Regenerate.

---
 gdb/config.in    | 3 ---
 gdb/configure    | 8 ++++----
 gdb/configure.ac | 2 +-
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/gdb/config.in b/gdb/config.in
index 26053475db..1aeb8603a1 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -505,9 +505,6 @@
 /* Define to 1 if you have the <sys/select.h> header file. */
 #undef HAVE_SYS_SELECT_H
 
-/* Define to 1 if you have the <sys/sockets.h> header file. */
-#undef HAVE_SYS_SOCKETS_H
-
 /* Define to 1 if you have the <sys/socket.h> header file. */
 #undef HAVE_SYS_SOCKET_H
 
diff --git a/gdb/configure b/gdb/configure
index c9a4b42ea1..adcfa49c63 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -11844,12 +11844,12 @@ fi
 done
 
 
-for ac_header in sys/sockets.h
+for ac_header in sys/socket.h
 do :
-  ac_fn_c_check_header_mongrel "$LINENO" "sys/sockets.h" "ac_cv_header_sys_sockets_h" "$ac_includes_default"
-if test "x$ac_cv_header_sys_sockets_h" = xyes; then :
+  ac_fn_c_check_header_mongrel "$LINENO" "sys/socket.h" "ac_cv_header_sys_socket_h" "$ac_includes_default"
+if test "x$ac_cv_header_sys_socket_h" = xyes; then :
   cat >>confdefs.h <<_ACEOF
-#define HAVE_SYS_SOCKETS_H 1
+#define HAVE_SYS_SOCKET_H 1
 _ACEOF
 
 fi
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 3bec21560e..620ae23e34 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1248,7 +1248,7 @@ AC_CHECK_HEADERS(term.h, [], [],
 #endif
 ])
 
-AC_CHECK_HEADERS([sys/sockets.h])
+AC_CHECK_HEADERS([sys/socket.h])
 AC_CHECK_HEADERS([ws2tcpip.h])
 
 # ------------------------- #