build: check MSG_NOSIGNAL directly, drop detection and interim macro

Drop detecting it at configure time, along with the interim macro
`HAVE_MSG_NOSIGNAL`. There is no longer a reason for this workaround,
and allows to save the work at configure time and simplify.

Also say in a comment that `sys/socket.h` is defining this macro.

Follow-up to 77b3bc239d

Closes #20559

CMake/OtherTests.cmake

@@ -50,19 +50,6 @@ if(NOT DEFINED HAVE_STRUCT_SOCKADDR_STORAGE)
   cmake_pop_check_state()
 endif()
 
-if(NOT WIN32)
-  set(_source_epilogue "#undef inline")
-  curl_add_header_include(HAVE_SYS_TYPES_H "sys/types.h")
-  check_c_source_compiles("${_source_epilogue}
-    #include <sys/socket.h>
-    int main(void)
-    {
-      int flag = MSG_NOSIGNAL;
-      (void)flag;
-      return 0;
-    }" HAVE_MSG_NOSIGNAL)
-endif()
-
 set(_source_epilogue "#undef inline")
 check_c_source_compiles("${_source_epilogue}
   #ifdef _MSC_VER

CMake/unix-cache.cmake

@@ -179,7 +179,6 @@ if(APPLE OR
 else()
   set(HAVE_MEMRCHR 1)
 endif()
-set(HAVE_MSG_NOSIGNAL 1)
 set(HAVE_NETDB_H 1)
 if(ANDROID)
   set(HAVE_NETINET_IN6_H 1)

CMake/win32-cache.cmake

@@ -125,7 +125,6 @@ set(HAVE_LINUX_TCP_H 0)
 set(HAVE_LOCALE_H 1)
 set(HAVE_LOCALTIME_R 0)
 set(HAVE_MEMRCHR 0)
-set(HAVE_MSG_NOSIGNAL 0)
 set(HAVE_NETDB_H 0)
 set(HAVE_NETINET_IN6_H 0)
 set(HAVE_NETINET_IN_H 0)

acinclude.m4

@@ -703,45 +703,6 @@ AC_DEFUN([CURL_CHECK_FUNC_SEND], [
   fi
 ])
 
-dnl CURL_CHECK_MSG_NOSIGNAL
-dnl -------------------------------------------------
-dnl Check for MSG_NOSIGNAL
-
-AC_DEFUN([CURL_CHECK_MSG_NOSIGNAL], [
-  AC_CHECK_HEADERS(sys/types.h)
-  AC_CACHE_CHECK([for MSG_NOSIGNAL], [curl_cv_msg_nosignal], [
-    AC_COMPILE_IFELSE([
-      AC_LANG_PROGRAM([[
-        #undef inline
-        #ifdef _WIN32
-        #ifndef WIN32_LEAN_AND_MEAN
-        #define WIN32_LEAN_AND_MEAN
-        #endif
-        #include <winsock2.h>
-        #else
-        #ifdef HAVE_SYS_TYPES_H
-        #include <sys/types.h>
-        #endif
-        #include <sys/socket.h>
-        #endif
-      ]],[[
-        int flag = MSG_NOSIGNAL;
-        (void)flag;
-      ]])
-    ],[
-      curl_cv_msg_nosignal="yes"
-    ],[
-      curl_cv_msg_nosignal="no"
-    ])
-  ])
-  case "$curl_cv_msg_nosignal" in
-    yes)
-      AC_DEFINE_UNQUOTED(HAVE_MSG_NOSIGNAL, 1,
-        [Define to 1 if you have the MSG_NOSIGNAL flag.])
-      ;;
-  esac
-])
-
 
 dnl CURL_CHECK_STRUCT_TIMEVAL
 dnl -------------------------------------------------

configure.ac

@@ -4127,7 +4127,6 @@ CURL_CHECK_FUNC_SELECT
 
 CURL_CHECK_FUNC_RECV
 CURL_CHECK_FUNC_SEND
-CURL_CHECK_MSG_NOSIGNAL
 
 CURL_CHECK_FUNC_ALARM
 CURL_CHECK_FUNC_BASENAME

lib/curl_config-cmake.h.in

@@ -400,9 +400,6 @@
 /* Define to 1 if you have the 'suseconds_t' data type. */
 #cmakedefine HAVE_SUSECONDS_T 1
 
-/* Define to 1 if you have the MSG_NOSIGNAL flag. */
-#cmakedefine HAVE_MSG_NOSIGNAL 1
-
 /* Define to 1 if you have the <netdb.h> header file. */
 #cmakedefine HAVE_NETDB_H 1
 

lib/curl_setup.h

@@ -852,7 +852,7 @@
 #endif
 
 #ifndef _WIN32
-#include <sys/socket.h>
+#include <sys/socket.h>  /* also for MSG_NOSIGNAL */
 #endif
 
 #include "functypes.h"
@@ -880,7 +880,7 @@ struct timeval {
  * If we have the MSG_NOSIGNAL define, make sure we use
  * it as the fourth argument of function send()
  */
-#ifdef HAVE_MSG_NOSIGNAL
+#ifdef MSG_NOSIGNAL
 #define SEND_4TH_ARG MSG_NOSIGNAL
 #else
 #define SEND_4TH_ARG 0

lib/multi.c

@@ -1852,7 +1852,7 @@ static void set_in_callback(struct Curl_multi *multi, bool value)
  */
 static void multi_posttransfer(struct Curl_easy *data)
 {
-#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(HAVE_MSG_NOSIGNAL)
+#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(MSG_NOSIGNAL)
   /* restore the signal handler for SIGPIPE before we get back */
   if(!data->set.no_signal)
     signal(SIGPIPE, data->state.prev_signal);

lib/transfer.c

@@ -535,7 +535,7 @@ CURLcode Curl_pretransfer(struct Curl_easy *data)
      * different ports! */
     data->state.allow_port = TRUE;
 
-#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(HAVE_MSG_NOSIGNAL)
+#if defined(HAVE_SIGNAL) && defined(SIGPIPE) && !defined(MSG_NOSIGNAL)
     /*************************************************************
      * Tell signal handler to ignore SIGPIPE
      *************************************************************/