The Silicon Labs IDE does not support the LX51 linker, only the the BL51 linker.
However, the LX51 linker may be used with µVision for projects less than 64k that do not require code banking.
The LX51 linker code packing option may result in a 3-8% code size reduction.
To use the LX51 linker with µVision and enable code packing:
When linking more than 64kB of program code on devices that use code banking, the BL51 linker must be used.