tests: posix: net: open native_sim in c++,posix,net,native case

Prior to the fixes in the previous commits, combining a build
for native_sim with

CONFIG_CPP=y
CONFIG_POSIX_API=y
CONFIG_STD_CPP20=y
CONFIG_REQUIRES_FULL_LIBCPP=y

would fail.

It succeeds now.

This change adds a testcase to monitor that scenario in CI.

Note: this was partially necessary because the deprecation of
CONFIG_NET_SOCKETS_POSIX_NAMES is not yet complete, so there
is a dependency cycle, and also because <sys/types.h> was
pulling in the host <sys/types.h> instead of Zephyr's or one
of the embedded OSes we support.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>

Author: cfriedt

tests/posix/net/testcase.yaml

@@ -1,15 +1,22 @@
 common:
   depends_on: netif
-  # native_sim uses if_*() from the native libc
-  filter: not CONFIG_NATIVE_LIBC
-  integration_platforms:
-    - qemu_x86
   min_ram: 16
-  platform_allow:
-    - qemu_x86
   tags:
     - iface
     - net
     - posix
 tests:
-  portability.posix.net: {}
+  portability.posix.net:
+    # native_sim links to if_*() from the host libc which causes the test to crash immediately.
+    filter: not CONFIG_NATIVE_LIBC
+  portability.posix.net.cpp.native_sim:
+    # demonstrate that #75319 fixes the build error in #75849
+    tags:
+      - cpp
+    build_only: true
+    platform_allow:
+      - native_sim
+    extra_configs:
+      - CONFIG_CPP=y
+      - CONFIG_STD_CPP20=y
+      - CONFIG_REQUIRES_FULL_LIBCPP=y