Force the alignment of SoA and AoS Particles (#4375)

This fixes build issues on 32-bit Linux. This should not affect 64 bits
machines.

Fix #4371

Author: WeiqunZhang

Src/Particle/AMReX_Particle.H

@@ -290,7 +290,7 @@ struct SoAParticleBase
  * \tparam T_NInt The number of extra integer components
  */
 template <int T_NReal, int T_NInt=0>
-struct Particle
+struct alignas(sizeof(double)) Particle
     : ParticleBase<ParticleReal,T_NReal,T_NInt>
 {
     static constexpr bool is_soa_particle = false;

Src/Particle/AMReX_ParticleTile.H

@@ -311,7 +311,7 @@ struct ParticleTileData
 
 // SOA Particle Structure
 template <int T_NArrayReal, int T_NArrayInt>
-struct ConstSoAParticle : SoAParticleBase
+struct alignas(sizeof(double)) ConstSoAParticle : SoAParticleBase
 {
     static constexpr int NArrayReal = T_NArrayReal;
     static constexpr int NArrayInt = T_NArrayInt;
@@ -373,7 +373,7 @@ struct ConstSoAParticle : SoAParticleBase
 };
 
 template <int T_NArrayReal, int T_NArrayInt>
-struct SoAParticle : SoAParticleBase
+struct alignas(sizeof(double)) SoAParticle : SoAParticleBase
 {
     static constexpr int NArrayReal = T_NArrayReal;
     static constexpr int NArrayInt = T_NArrayInt;