[tools/kconfig-frontends] append path for scons env (#5972)

tools/kconfig-frontends/SConstruct

 import os
 
 env = Environment()
+env.AppendENVPath('PATH', os.environ['PATH'])
 env['CPPPATH'] = ['libs/parser', 'libs']
 env['CPPDEFINES'] = ['CURSES_LOC=\\"ncurses.h\\"', 'HAVE_CONFIG_H', 
     'ROOTMENU=\\"Configuration\\"',