boot-monitor: pass custom LD var that includes sysroot option
boot-monitor: pass custom LD var that includes sysroot option

Otherwise it fails to link against static libgcc with OE toolchain.

Signed-off-by: Denys Dmytriyenko <d29de71aea38aad3a87d486929cb0aad173ae612@ti.com>

RedFIR/meta-ti,RedFIR/meta-ti,rcn-ee/meta-ti,rcn-ee/meta-ti,joelagnel/meta-ti,rcn-ee/meta-ti,tylerwhall/meta-ti,tylerwhall/meta-ti,joelagnel/meta-ti,RedFIR/meta-ti,tylerwhall/meta-ti,RedFIR/meta-ti,joelagnel/meta-ti,tylerwhall/meta-ti,joelagnel/meta-ti,rcn-ee/meta-ti