Hi, Conrad,
From hardware perspective, the LPC54113 had two cores:Cortex-M4 and Cortex-M0, after Reset, the cortex-M4 begins to run, so the code of startup_lpc5411x.c is for Cortex-M4 rather than Cortex-M0.
If you want to start Cortex-M0, the Cortex-M4 has to write register for example give start address of M0 to start Cortex-M0.
Hope it can help you
BR
Xiangjun Rong