ARM: Fix signed/unsigned simd mismatch in vbool4::load

Fixes 3721

Please read the comments in 3721. This is the "local" fix for the
build break due to the type mismatch. It is a band-aid. And it may be
the best solution for the 2.4 branch if we don't want to potentially
break ABIs by changing the definition of any public types.

Still pending is to examine the issue of whether it was a mistake to
define vbool4 storage for neon as uint32x4_t or if we should change it
to int32x4_t to better match the non-simd reference implementation.
After debating that (and identifying somebody with access to an
ARM-based machine to test the solution for us), we may return to
tackle this more fundamental change.

Author: lgritz

src/include/OpenImageIO/simd.h

@@ -3261,7 +3261,9 @@ OIIO_FORCEINLINE void vbool4::load (bool a, bool b, bool c, bool d) {
     m_simd = _mm_castsi128_ps(_mm_set_epi32(-int(d), -int(c), -int(b), -int(a)));
 #elif OIIO_SIMD_NEON
     int values[4] = { -int(a), -int(b), -int(c), -int(d) };
-    m_simd = vld1q_s32 (values);
+    m_simd = vld1q_u32((const uint32_t*)values);
+    // this if we were using int:
+    // m_simd = vld1q_s32(values);
 #else
     m_val[0] = -int(a);
     m_val[1] = -int(b);