Please do the following:
1) tar jxvf u-boot-1.1.4.tar.bz2
2) mv u-boot-1.1.4 u-boot-3.4.16
3) unzip u-boot-3.4.16 (this will overwriting existing files)
4) cd u-boot-3.4.16
5) make mrproper
6) make rd88f6281Sheevaplug_config NBOOT=1 LE=1
The output should be u-boot-rd88f6281Sheevaplug_400db_nand.bin
The final instruction to compile U-Boot is "make all", not make. This will fix your compile errors.
edit: this ought
to fix your compile errors. it fixed my mainline u-boot compile errors, at least, which looked very very very similar to the errors you are experiencing.
edit2: my undefined reference was at a latter step, never mind. still, the mainline uboot sequence is make board_config; make all;