Fix conditional jump over jmp (X86/X86-64/ARM32)

Optimize the code generation for 'if' statements to jump to the
'false' block if the next block to be generated is the 'true' block.

Add an X86-64 test for this case.

Note that ARM64 & MIPS64 have not been updated.

Change-Id: Iebb1352feb9d3bd0142d8b0621a2e3069a708ea7
Signed-off-by: Mark Mendell <mark.p.mendell@intel.com>