BT_USE_NEON fails to build on Linux

[glebm]

Linking statically, built from HEAD, with -DBT_USE_NEON=1 and GCC10, for Linux:

ld: /tmp/openmw.RFu4sG.ltrans16.ltrans.o: in function `btVector3::maxDot(btVector3 const*, long, float&) const':
<artificial>:(.text+0xfaa294): undefined reference to `_maxdot_large'
ld: <artificial>:(.text+0xfaa298): undefined reference to `_maxdot_large'
collect2: error: ld returned 1 exit status

If I also set -DBT_USE_SIMD_VECTOR3=1, I instead get a compile error:

src/LinearMath/btVector3.cpp:857:13: error: ‘sysctlbyname’ was not declared in this scope
  857 |   int err = sysctlbyname("hw.optional.neon_hpfp", &hasFeature, &featureSize, NULL, 0);

Looks like it's using some Apple / BSD specific syscall that doesn't exist on Linux

Modifying it to remove the syscall results in another error:

{standard input}:7217301: Error: instruction does not accept this addressing mode -- `vld1.f32 {d16},[r2,#128]!'