Add lib/bdf-plugins

[Liviu Ionescu]

Probably due to a misunderstanding, some of the binutils search for the plugins in a different folder than creaded by GCC.

Thus attempts to use traditional executable names with LTO fail.

$ arm-none-eabi-ar -r "libarm-static-lib.a" ./lib.o
arm-none-eabi-ar: creating libarm-static-lib.a
arm-none-eabi-ar: ./lib.o: plugin needed to handle lto object <---

I know that the new fashion is to use arm-none-eabi-gcc-ar, but there are still lots of old environments that use the traditional name.

The solution is easy, a folder named bdf-plugins must be created in lib and a link to the liblto_plugin shared library must be added.

FYI, the xPack GNU Embedded ARM GCC (formerly GNU MCU Eclipse ARM Embedded GCC) binaries successfully use this extra folder and avoid these errors.