Unaligned access in `initGcThreads`?

While attempting to build a ARMv7 bindist for %9.2.2 I found that GHC would throw a bus error under certain conditions.

The culprit appears to be

Thread 1 "ghc-stage2" received signal SIGBUS, Bus error.
init_gc_thread (t=0x1e737b8) at rts/sm/GC.c:1872
1872        t->copied = 0;
(gdb) disassemble 
Dump of assembler code for function initGcThreads:
   0xef486334 <+0>:     push    {r4, r5, r6, r7, r8, r9, r10, r11, lr}
   0xef486338 <+4>:     sub     sp, sp, #4
...
   0xef4864a4 <+368>:   ldr     r1, [pc, #360]  ; 0xef486614 <initGcThreads+736>
   0xef4864a8 <+372>:   ldr     r1, [pc, r1]
   0xef4864ac <+376>:   str     r1, [r2, #24]
   0xef4864b0 <+380>:   str     r1, [r2, #20]
   0xef4864b4 <+384>:   add     r1, r2, #48     ; 0x30
   0xef4864b8 <+388>:   ldr     r0, [r0, #900]  ; 0x384
=> 0xef4864bc <+392>:   vst1.64 {d8-d9}, [r1 :128]
   0xef4864c0 <+396>:   mov     r1, #256        ; 0x100
   0xef4864c4 <+400>:   strh    r1, [r2, #44]   ; 0x2c
   0xef4864c8 <+404>:   str     r8, [r2, #40]   ; 0x28
...
(gdb) print/x $r1
$2 = 0x1e737e8

vst is apparently a NEON instruction and this particular encoding appears to require 16 byte alignment, which is clearly not satisfied.

Frankly, I suspect that this may be a clang-13 bug (which is the compiler that I used to bootstrap) as this is C code and surely it should not have chosen this encoding unless it could prove that the pointer is sufficiently aligned.