The -march flag permits the compiler to use instructions that are not supported by other CPUs. There are a few instructions that are legal to use with
-march=athlon64 that your i7 does not support. These are the 3DNow! and Enhanced 3DNow! instructions that weren't included in MMX or integer SSE. If the code uses instructions like PFPNACC it will fault on your i7.
That said, it's extremely unlikely that it actually does use any such instructions because those instructions have generally been found to be of little use -- the useful 3DNow! instructions were incorporated into MMX or iSSE, which your CPU does support.
So it's not guaranteed to work, but it probably will.
-march=cpu-type: Generate instructions for the machine type
-march=cpu-type allows GCC to generate code that may not run at all on processors other than the one indicated.