7.0.3 segfault on aarch64
Imported issue: Initially reported by Jerry James in https://gforge.inria.fr/tracker/?group_id=135&aid=20712
See https://bugzilla.redhat.com/show_bug.cgi?id=1367571 for more information. The 7.0.3 build is segfaulting on aarch64 machines while running the test suite. From information provided by valgrind, it appears that inside mpres_pow(), K = 4, and therefore 16 bytes are allocated for B, but then w becomes 10 inside the following loop, so the call to mpres_pow_mul passes B[w/2] == B[5], but only indices 0 through 3 are valid.