Don't look for files under `/usr/include' since we don't have that directory
under NixOS.

--- gnu-ghostscript-8.64.0/base/unix-aux.mak	2009-04-19 19:00:20.000000000 +0200
+++ gnu-ghostscript-8.64.0/base/unix-aux.mak	2009-04-27 11:58:31.000000000 +0200
@@ -103,13 +103,13 @@ $(MKROMFS_XE): $(GLSRC)mkromfs.c $(MKROM
 # The "else true;" is required because Ultrix's implementation of sh -e
 # terminates execution of a command if any error occurs, even if the command
 # traps the error with ||.
-INCLUDE=/usr/include
+INCLUDE=/no-such-path
 $(gconfig__h): $(UNIX_AUX_MAK) $(ECHOGS_XE)
 	$(ECHOGS_XE) -w $(gconfig__h) -x 2f2a -s This file was generated automatically by unix-aux.mak. -s -x 2a2f
-	if ( test -f $(INCLUDE)/dirent.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_DIRENT_H; else true; fi
-	if ( test -f $(INCLUDE)/ndir.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_NDIR_H; else true; fi
-	if ( test -f $(INCLUDE)/sys/dir.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_DIR_H; else true; fi
-	if ( test -f $(INCLUDE)/sys/ndir.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_NDIR_H; else true; fi
-	if ( test -f $(INCLUDE)/sys/time.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_TIME_H; else true; fi
-	if ( test -f $(INCLUDE)/sys/times.h ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_TIMES_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_DIRENT_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_NDIR_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_DIR_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_NDIR_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_TIME_H; else true; fi
+	if ( true ); then $(ECHOGS_XE) -a $(gconfig__h) -x 23 define HAVE_SYS_TIMES_H; else true; fi
 	if ( test -f $(JSRCDIR)/jmemsys.h); then true; else $(ECHOGS_XE) -a $(gconfig__h) -x 23 define DONT_HAVE_JMEMSYS_H; fi