typed arrays: swizzle with compiler intrinsics

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