Remove -march=i686 on Raspberry Pi

remove the -march=i686 argument when compiling for the Raspberry Pi; otherwise it ends with the following error:

pi@owncloud ~ $ cd adchpp/
pi@owncloud ~/adchpp $ scons
scons: Reading SConscript files ...
Checking for C header file poll.h... (cached) no
Checking for C header file sys/epoll.h... (cached) no
Checking for pthread_create() in C library pthread... (cached) no
Checking for SSL_connect() in C library ssl... (cached) no
Checking for dlopen() in C library dl... (cached) no
Copy("/home/pi/adchpp/build/debug-default/bin/lua", "lua")
scons: *** /home/pi/adchpp/build/debug-default/bin/lua: File exists
[Errno 2] No such file or directory
Ruby not found, skipping ruby module
Python.h not found, not building python extension
scons: done reading SConscript files.
scons: Building targets ...
Compiling build/debug-default/adchpp/adchpp.h.gch (shared precompiled header)
cc1plus: error: bad value (i686) for -march switch
scons: *** [build/debug-default/adchpp/adchpp.h.gch] Error 1
scons: building terminated because of errors.