evio: workaround for wsl1 so_linger assertion

SO_LINGER makes no much sense for unix-sockets, and Microsoft WSL
is returning EINVAL if setsockopts called for SO_LINGER over unix
sockets:

  [004] 2020-03-11 18:42:29.592 [29182] main/102/app sio.c:169 !> SystemError setsockopt(SO_LINGER), called on fd 16, aka
  [004] 2020-03-11 18:42:29.592 [29182] main/102/app F> can't initialize storage: setsockopt(SO_LINGER), called on fd 16,
  [004] 2020-03-11 18:42:29.592 [29182] main/102/app F> can't initialize storage: setsockopt(SO_LINGER), called on fd 16,

And it's sort of correct here, but the problem is Linux is simply
silently ignoring it, which passes tests.

After much debates we decided to work-around this case via CMAKE
define.

NB! In a future (April/May 2020), when WSL2 with full Linux kernel
would be released we should disable this check.

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>

cmake/os.cmake

@@ -11,6 +11,15 @@ if (${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
 # (see man page for feature_test_macros).
     add_definitions("-D_FILE_OFFSET_BITS=64")
     find_package_message(PLATFORM "Building for Linux" "${CMAKE_SYSTEM_NAME}")
+
+    # There are some subtle differences in Linux kernel calls
+    # implementation under WSL1 (which should go away with WSL2 kernel)
+    # so for a moment we introduce a way to distinguish Linux and
+    # Microsoft/WSL1
+    if (${CMAKE_SYSTEM} MATCHES "Linux-.*-Microsoft")
+        add_definitions("-DTARANTOOL_WSL1_WORKAROUND_ENABLED=1")
+    endif()
+
 elseif (${CMAKE_SYSTEM_NAME} STREQUAL "kFreeBSD")
     set(TARGET_OS_FREEBSD 1)
     set(TARGET_OS_DEBIAN_FREEBSD 1)

src/lib/core/evio.c

@@ -140,6 +140,7 @@ evio_setsockopt_server(int fd, int family, int type)
 		       &on, sizeof(on)))
 		return -1;
 
+#ifndef TARANTOOL_WSL1_WORKAROUND_ENABLED
 	/* Send all buffered messages on socket before take
 	 * control out from close(2) or shutdown(2). */
 	struct linger linger = { 0, 0 };
@@ -147,6 +148,7 @@ evio_setsockopt_server(int fd, int family, int type)
 	if (sio_setsockopt(fd, SOL_SOCKET, SO_LINGER,
 		       &linger, sizeof(linger)))
 		return -1;
+#endif
 	if (type == SOCK_STREAM && family != AF_UNIX &&
 	    evio_setsockopt_keepalive(fd) != 0)
 		return -1;