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>

 # MIPS specific config options

 config ARCH_mips

     select ARCH_SUPPORTS_32

     select ARCH_SUPPORTS_64 if EXPERIMENTAL

     select ARCH_DEFAULT_32

     select ARCH_USE_MMU

     select ARCH_SUPPORTS_BOTH_ENDIAN

     select ARCH_DEFAULT_BE

     select ARCH_SUPPORT_ARCH

     select ARCH_SUPPORT_TUNE

     help

       The MIPS architecture, as defined by:

         http://www.mips.com/