Improve infrastructure for dealing with endianness in VEX.  This patch
removes all decisions about endianness from VEX.  Instead, it requires
that the LibVEX_* calls pass in information about the guest or host
endianness (depending on context) and in turn it passes that info
through to all the places that need it:

* the front ends (xx_toIR.c)
* the back ends (xx_isel.c)
* the patcher functions (Chain, UnChain, PatchProfInc)

Mostly it is boring and ugly plumbing.  As far as types go, there is a
new type "VexEndness" that carries the endianness.  This also makes it
possible to stop using Bools to indicate endianness.  VexArchInfo has
a new field of type VexEndness.  Apart from that, no other changes in
types.

Followups: MIPS front and back ends have not yet been fixed up to use
the passed-in endianness information.  Currently they assume that the
endianness of both host and guest is the same as the endianness of the
target for which VEX is being compiled.



git-svn-id: svn://svn.valgrind.org/vex/trunk@2910 8f6e269a-dfd6-0310-a8e1-e2731360e62c