Resolving this issue depends largely on the specific compiler toolset and the associated IDE utilized to develop your code.
If you are using the XC16 compiler in combination with the MPLAB X, simply adding the libraries to the current project library folder may or may not automatically cue the MPLAB X IDE to insert the proper -l options into for linker command line configuration. However, as Susan pointed out they need to be present, one way or another, therefore check the actual linkage commands issued in the appropriate Output window or check the appropriate Project Properties settings, XC16-ld, Option Categories: Libraries -> Libraries and Library Directories.
Please note, as these are COFF libraries, you will need to ensure the Object Model Format is set to COFF, not the default ELF/DWARF.
You can change these settings under the Project Properties Settings Window:
On the right hand side, Categories: XC16 Global Options -> On the left hand side, Options for XC16-GCC, Option Categories: drop down menu, Global Options, beneath, Output File Format -> drop down menu, COFF.
Or you could elect to utilize the ELF versions, libq-dsp-elf.a and the libdsp-elf.a instead and retain the default OMF of ELF/DWARF.
BigDog