...the ~/.xprofile is probably not the best place to put those commands.
If you are using bash as your shell, you shold have this file
There should be even more: ~/.bashrc ~/.bash_profile ~/.bash_history ~/.alias
If they are not there - you are using the settings from your globlal config-files in /etc then...
They are: /etc/bashrc /etc/profile /etc/environment
About the way to use these variables:
if you do not know how to initialize those variables (via ~/.bash_profile or ~/.bashrc) it is easiest and best to do it from command line!
You do not have to issue these commands every time over and over again!
You need to do it just once for every terminal you open and want to have those variables available.
If you do'nt want them anymore - you do not have to close that terminal but to clear the variables:
and everything is back as it was...
./configure probably does tell you...
But it is a script that is designed to configure the source tree for you - among other things it changes Makefiles - and there you find that it put in the options you gave it - the configure script has next to nothing to do with compiling - that comes later
If you want to know, what the option "-march=atlon-xp" does - as well as the other ones - there is only one place I know of to surely find this information for your compiler:
here are the important lines:
Tune to cpu-type everything applicable about the generated code, except for the ABI and the set of available instructions. The choices for cpu-type are i386, i486, i586, i686, pentium, pentium-mmx, pentiumpro, pentium2, pentium3, pentium4, k6, k6-2, k6-3, athlon, athlon-tbird, athlon-4, athlon-xp, athlon-mp, winchip-c6, winchip2 and c3.
While picking a specific cpu-type will schedule things appropriately for that particular chip, the compiler will not generate any code that does not run on the i386 without the -march=cpu-type option being used. i586 is equivalent to pentium and i686 is equivalent to pentiumpro. k6 and athlon are the AMD chips as opposed to the Intel ones.
Generate instructions for the machine type cpu-type. The choices for cpu-type are the same as for -mcpu. Moreover, specifying -march=cpu-type implies -mcpu=cpu-type.
...that's why you only need to give -march=... (added by me)