Reason: error(3) does not exist on musl, and on glibc the signature
is (int, int, char*, ...) and not (char*, ...).
Therefore the current code either results in garbled output or
doesn't work at all. Replace it with a simple printf.

---
--- a/DisplayCAL/RealDisplaySizeMM.c	2018-07-25 16:47:01.000000000 +0200
+++ b/DisplayCAL/RealDisplaySizeMM.c	2018-07-25 16:47:01.000000000 +0200
@@ -822,13 +822,13 @@
 						sprintf(desc1, "_ICC_PROFILE_%d",disps[ndisps]->uscreen);
 
 					if ((disps[ndisps]->icc_atom = XInternAtom(mydisplay, desc1, False)) == None)
-						error("Unable to intern atom '%s'",desc1);
+						fprintf(stderr, "Unable to intern atom '%s'",desc1);
 
 					debugrr2((errout,"Root atom '%s'\n",desc1));
 
 					/* Create the atom of the output that may contain the associated ICC profile */
 					if ((disps[ndisps]->icc_out_atom = XInternAtom(mydisplay, "_ICC_PROFILE", False)) == None)
-						error("Unable to intern atom '%s'","_ICC_PROFILE");
+						fprintf(stderr, "Unable to intern atom '%s'","_ICC_PROFILE");
 		
 					/* Grab the EDID from the output */
 					{
@@ -993,7 +993,7 @@
 				sprintf(desc1, "_ICC_PROFILE_%d",disps[i]->uscreen);
 
 			if ((disps[i]->icc_atom = XInternAtom(mydisplay, desc1, False)) == None)
-				error("Unable to intern atom '%s'",desc1);
+				fprintf(stderr, "Unable to intern atom '%s'",desc1);
 
 			/* See if we can locate the EDID of the monitor for this screen */
 			for (j = 0; j < 2; j++) { 
