MDEV-27758: Errors when building Connect engine on os x 11.6.2

Added checking for support of vfork by a platform where
building being done. Set HAVE_VFORK macros in case vfork()
system call is supported. Use vfork() system call if the
macros HAVE_VFORK is set, else use fork().

config.h.cmake

@@ -577,3 +577,5 @@
 #endif  // !defined(__STDC_FORMAT_MACROS)
 
 #endif
+
+#cmakedefine HAVE_VFORK 1

configure.cmake

@@ -1033,3 +1033,19 @@ IF(NOT MSVC)
   HAVE_FALLOC_PUNCH_HOLE_AND_KEEP_SIZE
   )
 ENDIF()
+
+MY_CHECK_C_COMPILER_FLAG("-Werror")
+IF(have_C__Werror)
+  SET(SAVE_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+  SET(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -Werror")
+  CHECK_C_SOURCE_COMPILES("
+    #include <unistd.h>
+    int main()
+    {
+      pid_t pid=vfork();
+      return (int)pid;
+    }"
+    HAVE_VFORK
+  )
+  SET(CMAKE_REQUIRED_FLAGS ${SAVE_CMAKE_REQUIRED_FLAGS})
+ENDIF()

storage/connect/tabrest.cpp

@@ -112,7 +112,11 @@ int Xcurl(PGLOBAL g, PCSZ Http, PCSZ Uri, PCSZ filename)
 
 	} // endif f
 	
-	pID = vfork();
+#ifdef HAVE_VFORK
+       pID = vfork();
+#else
+       pID = fork();
+#endif
 	sprintf(fn, "-o%s", filename);
 
 	if (pID == 0) {