On my laptop (i7-5500U), I get the following timings (always with -march=native or -xHOST):

    GCC 6.3, -Ofast:      5.93s
    GCC 6.3, -O3:        93.06s
    GCC 6.3, -O2:       134.43s
    Clang 3.9, -O3:     346.92s
    Clang 3.9, -Ofast:    5.87s
    Intel 15.0, -O3:    110.84s
    Intel 15.0, -Ofast: 106.88s

The Intel compiler is relatively old, but mostly it seems to be a case of IEEE 754 conformance -- if enabled, things take longer, if disabled, they’re (probably) as fast in C as in Rust.