The options are based on varied options for MicroBlaze, particularly barrel shifting, multiplier, and little endian. Depending on what settings you use, libgen will call the appropriate libc. In short, the following will be called:
microblaze-xilinx-elf\lib\libc.a <==No flags microblaze-xilinx-elf\lib\bs\libc.a <== Barrel Shifting only microblaze-xilinx-elf\lib\le\libc.a <== Little Endian only microblaze-xilinx-elf\lib\m\libc.a <==Multiplier only microblaze-xilinx-elf\lib\bs\le\libc.a <==Barrel Shifting AND Little Endian microblaze-xilinx-elf\lib\bs\m\libc.a <==Barrel Shifting AND Multiplier microblaze-xilinx-elf\lib\m\le\libc.a <== Multiplier AND Little Endian microblaze-xilinx-elf\lib\bs\m\le\libc.a <==Barrel shifting AND Multiplier AND Little Endian