the_gc_thread variable from GC.c is not aligned to 64

When compiling GHC with clang and -march=native flag, the compiler emits vmovaps instruction with unaligned operand for this code:

* thread #1, name = 'ghc-pkg', stop reason = signal SIGBUS: hardware error
    frame #0: 0x0000000804e476c6 libHSrts-ghc8.0.2.so`initGcThreads [inlined] new_gc_thread(n=0) at GC.c:818
   815          ws->todo_q = newWSDeque(128);
   816          ws->todo_overflow = NULL;
   817          ws->n_todo_overflow = 0;
-> 818          ws->todo_large_objects = NULL;
   819 
   820          ws->part_list = NULL;
   821          ws->n_part_blocks = 0;

Research done by another FreeBSD developer suggested that this is due

StgWord8 the_gc_thread[sizeof(gc_thread) + 64 * sizeof(gen_workspace)];

not being aligned to 64 bytes, because struct gc_thread have no alignment specifier.

Detailed information can be found in FreeBSD bugzilla: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=226059

Trac metadata

Trac field	Value
Version	8.4.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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