GCC Error Referencing re_comp & re_exec

I've been trying to compile an older network monitoring utility called Rover on a NetBSD system, but keep getting errors about re_comp and re_exec. The errors are as follows:
display.o: In function `AddFilter':
display.o(.text+0xd5): undefined reference to `re_comp'
display.o: In function `CountProblem':
display.o(.text+0x66b): undefined reference to `re_comp'
display.o(.text+0x67a): undefined reference to `re_exec'
display.o: In function `FilterProblem':
display.o(.text+0x707): undefined reference to `re_comp'
display.o(.text+0x716): undefined reference to `re_exec'

If someone can help me figure out these errors that would be great.

Thanks.