[ODE] Architecture tunning

[Rodrigo Hernandez]

I just added the option --with-arch= to the configure script, this is an 
optional algument to configure and just adds the flag -march= to gcc CPP 
Flags, enabling the use of
the architecture extensions such as MMX or SSE by the compiler.

the usage for example for a Pentium 4 would be:

configure --with-arch=pentium4

for an Athlon XP:

configure --with-arch=athlon-xp

for a list of all posible options check:

http://gcc.gnu.org/onlinedocs/gcc-3.4.1/gcc/i386-and-x86-64-Options.html#i386%20and%20x86-64%20Options

Note that that page lists the architecture posibilities for Intel based 
processors, but other architectures such as MIPS also have support for 
the -march flag.

Cheers!