makefile: replace unnecessary use of xargs

[davidchambers]

Questions:

• Is there any value in quoting filenames in this context? After reading GNU Make meets file names with spaces in them I'm don't think there's much hope of correctly handling filenames containing spaces.
• Is there a reason to favour this two-step process over $(COFFEE) -co $(@D) $<? The latter would obviate the need for mkdir on our part.

[michaelficarra]

Is there any value in quoting filenames in this context?

Yes. I'm not using spaces explicitly anywhere in the Makefile, and the variables I'm using safely handle spaces.

Is there a reason to favour this two-step process

CSR does not automatically create a directory for the output file if it does not exist.

[davidchambers]

CSR does not automatically create a directory for the output file if it does not exist.

Good to know.