tclibc-baremetal: Supply missing /bin/sh target in the baremetal sdk

SDK recipes now require a provider for /bin/sh, this
should come from nativesdk-sdk-provides-dummy which
is added by default to Linux SDKs, however tclibc-baremetal
requires us to explicitly add its new dependency to
TOOLCHAIN_HOST_TASK, otherwise we get a packaging error
while generating an SDK.

e.g.
package packagegroup-cross-canadian-qemuriscv32-1.0-r0.x86_64_nativesdk
requires gdb-cross-canadian-riscv32, but none of the providers
can be installed
  - conflicting requests
  - nothing provides /bin/sh needed by
    gdb-cross-canadian-riscv32-11.1-r0.x86_64_nativesdk

Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>