typed arrays: undo local changes

Partially revert 5664dd2, 6573fc3 and 7788a6b to ease landing changes
from upstream.
typed arrays: swizzle with compiler intrinsics

Implement swizzling with compiler intrinsics and be aware of the native
endianness to correctly swap on big endian machines.

This introduces a template function to swap the bytes of a value,
and macros for the low level swap (taking advantage of gcc and msvc
intrinsics). This produces code like the following (comments are mine):

gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)

setValue<double>:
  movd  %xmm0, %rax         ; fp reg -> gen reg
  bswapq  %rax              ; 64-bit byte swap
  movd  %rax, %xmm0         ; gen reg -> fp reg
  movq  %xmm0, (%r15,%r12)  ; store
typed arrays: implement load and store swizzling

Implement load and store swizzling operations. This reduces an unneeded
back and forth between types and additionally keeps the value in the
swappable type until it is swapped. This is important for correctness
when dealing with floating point, to avoid the possibility of loading
the bits of a signaling NaN (because it isn't yet swapped) into the FPU.

This additionally produces better code (comments are mine):

gcc version 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)

setValue<double>:
  movd  %xmm0, %rax         ; fp reg -> gen reg
  bswapq  %rax              ; 64-bit byte swap
  movq  %rax, (%r15,%r12)   ; store