libxl: permit declaration after statement

libxl: permit declaration after statement

GCC and C99 allow declarations to be mixed with code.  This is a good
idea because:

 * It allows variables to be more often initialised as they are
   declared, thus reducing the occurrence of uninitialised variable
   errors.

 * Certain alloca-like constructs (arrays allocated at runtime on the
   stack) can more often be written without a spurious { } block.
   Such blocks are confusing to read.

 * It makes it easier to write and use macros which declare and
   initialise formulaic variables and do other function setup code,
   because there is no need to worry that such macros might be
   incompatible with each other or have strict ordering constraints.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>