[libc]解决龙芯内置工具链没有sys/select.h的问题

components/libc/compilers/common/partial/SConscript

+# RT-Thread building script for bridge
+
+import os
+from building import *
+
+cwd = GetCurrentDir()
+objs = []
+list = os.listdir(cwd)
+
+for d in list:
+    path = os.path.join(cwd, d)
+    if os.path.isfile(os.path.join(path, 'SConscript')):
+        objs = objs + SConscript(os.path.join(d, 'SConscript'))
+
+Return('objs')

components/libc/compilers/common/partial/ls1/SConscript

+from shutil import copy
+from building import *
+
+Import('rtconfig')
+
+src   = []
+cwd   = GetCurrentDir()
+CPPPATH = [cwd]
+group = []
+
+# There is no 'sys/select.h' in these bsp's gcc toolchain; thus, we need to copy this file from 'nogcc/sys/select.h'
+if GetDepend('SOC_LS1B') or GetDepend('SOC_LS1C300'):
+    copy("../../nogcc/sys/select.h", "sys/select.h")
+    if GetDepend('RT_USING_LIBC'):
+        src += Glob('*.c')
+    group = DefineGroup('libc', src, depend = [], CPPPATH = CPPPATH)
+
+Return('group')