feature-arm-thumb.inc: respect ARM_INSTRUCTION_SET when adding thumb suffix

* this means that recipes with ARM_INSTRUCTION_SET explicitly changed
  to arm will be built in feed without thumb suffix, the same does apply
  for workdir, e.g. after "bitbake glib-2.0" you can see:

  tmp-glibc/work/armv5e-oe-linux-gnueabi:
  glib-2.0  glibc  glibc-initial

  tmp-glibc/work/armv5te-oe-linux-gnueabi:
  acl              db              gdk-pixbuf     kmod  ....

  and

  tmp-glibc/deploy/ipk:
  all  armv5e  armv5te  qemuarm

* feed config should be ok, because all default DEFAULTTUNEs always
  include "arm" variants of all supported PACKAGE_ARCHs

* for more details see
  http://lists.openembedded.org/pipermail/openembedded-core/2014-April/091960.html


  the toolchain path issues were resolved in 1.8

* add ARM_INSTRUCTION_SET = "arm" to glibc-collateral.inc and comment in
  glibc.inc to fix glibc-locale and glibc-scripts build

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>