fixes basic type alignement issue on i386 platform. (#6209)

compiler/semtypes.nim

@@ -1512,9 +1512,26 @@ proc semTypeNode(c: PContext, n: PNode, prev: PType): PType =
     dec c.inTypeContext
 
 proc setMagicType(m: PSym, kind: TTypeKind, size: int) =
+  # source : https://en.wikipedia.org/wiki/Data_structure_alignment#x86
   m.typ.kind = kind
-  m.typ.align = size.int16
   m.typ.size = size
+  # this usually works for most basic types
+  # Assuming that since ARM, ARM64  don't support unaligned access
+  # data is aligned to type size
+  m.typ.align = size.int16
+
+  # FIXME: proper support for clongdouble should be added.
+  # long double size can be 8, 10, 12, 16 bytes depending on platform & compiler
+  if targetCPU == cpuI386 and size == 8:
+    #on Linux/BSD i386, double are aligned to 4bytes (except with -malign-double)
+    if kind in {tyFloat64, tyFloat} and
+       targetOS in {osLinux, osAndroid, osNetbsd, osFreebsd, osOpenbsd, osDragonfly}:
+      m.typ.align = 4
+    # on i386, all known compiler, 64bits ints are aligned to 4bytes (except with -malign-double)
+    elif kind in {tyInt, tyUInt, tyInt64, tyUInt64}:
+      m.typ.align = 4
+  else:
+    discard
 
 proc processMagicType(c: PContext, m: PSym) =
   case m.magic