SIGILL (Illegal instruction) in `mpn_mul_1` ADX/BMI2 path on CPU without ADX (Intel Haswell / i7-4790)

[Torbjörn Granlund]

If GMP is configured for CPU x and then run on CPU y, and CPU y lacks
some CPU x instructions used by GMP, then GMP cannot be expected to
work.

If, on the other hand, GMP was configured with --enable-fat, it is
expected that everyting will work fine, albeit with some overhead.

Obviously, any program or library which is compiled for CPU x and then
run on CPU y might also trigger "illegal instruction" errors.

-- 
Torbjörn
Please encrypt, key id 0xC8601622