config: add option to build statically linked toolchain

Add a config option to statically build the host tools.
Impacted tools can use that option to decide wether to build
statically or shared.

For now, no tool uses it, but they'll be added one at a time
in the next commits.

Signed-off-by: "Bryan Hundven" <bryanhundven@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Blackfin specific configuration file

config ARCH_blackfin

    select ARCH_SUPPORTS_32

    select ARCH_DEFAULT_32

    select ARCH_DEFAULT_LE

    select ARCH_SUPPORT_ARCH

    select ARCH_SUPPORT_CPU

    select ARCH_SUPPORT_TUNE

    select ARCH_SUPPORT_FPU

     help

      The Blackfin architecture