add sys_wait_h (#2960)

packages/s/sys_wait_h/xmake.lua

@@ -0,0 +1,16 @@
+package("sys_wait_h")
+    set_kind("library", {headeronly = true})
+    set_homepage("https://github.com/win32ports/sys_wait_h")
+    set_description("header-only Windows implementation of the <sys/wait.h> header")
+    set_license("MIT")
+
+    add_urls("https://github.com/win32ports/sys_wait_h.git")
+    add_versions("2019.05.12", "229dee8de9cb4c29a3a31115112a4175df84a8eb")
+
+    on_install("windows", function (package)
+        os.cp("sys", package:installdir("include"))
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("wait", {includes = "sys/wait.h"}))
+    end)