Add the system call epoll (#7893)

components/libc/posix/Kconfig

@@ -31,6 +31,13 @@ if RT_USING_POSIX_FS
         select RT_USING_POSIX_POLL
         default n
 
+    if RT_USING_SMART
+        config RT_USING_POSIX_EPOLL
+            bool "Enable I/O Multiplexing epoll <sys/epoll.h>"
+            select RT_USING_POSIX_POLL
+            default n
+    endif
+
     config RT_USING_POSIX_SOCKET
         bool "Enable BSD Socket I/O <sys/socket.h> <netdb.h>"
         select RT_USING_POSIX_SELECT

components/libc/posix/io/epoll/SConscript

@@ -0,0 +1,14 @@
+# RT-Thread building script for component
+
+from building import *
+
+cwd     = GetCurrentDir()
+src     = []
+CPPPATH = [cwd]
+
+if GetDepend('RT_USING_POSIX_EPOLL'):
+    src += ['epoll.c']
+
+group = DefineGroup('POSIX', src, depend = [''], CPPPATH = CPPPATH)
+
+Return('group')