By default, Nim stores intermediate object files in ~/.cache/nim.  patch moves
the nimcache into the working directory of the guix build.  This should not be
needed past version 0.4.4 of Chawan.

diff --git a/Makefile b/Makefile
index 8f538522..6ffc8149 100644
--- a/Makefile
+++ b/Makefile
@@ -227,7 +227,7 @@ $(OUTDIR_LIBEXEC)/urldec: $(OUTDIR_LIBEXEC)/urlenc
 
 # Do not add FLAGS here, because that breaks cross-compilation.
 $(OBJDIR)/chac: src/chac.nim lib/monoucha0/monoucha/* lib/monoucha0/monoucha/qjs/*
-	$(NIMC) -o:$@ $<
+	$(NIMC) --nimcache:"$(OBJDIR)/chac_cache" -o:$@ $<
 
 $(OUTDIR_LIBEXEC)/%.jsb: src/%.js $(OBJDIR)/chac
 	$(OBJDIR)/chac $(chac_flags) $< $@
@@ -314,7 +314,7 @@ uninstall:
 	for f in $(manpages1); do rm -f "$(DESTDIR)$(MANPREFIX1)/$$f"; done
 
 test/net/run: test/net/run.nim
-	$(NIMC) test/net/run.nim
+	$(NIMC) --nimcache:"$(OBJDIR)/test_net" test/net/run.nim
 
 .PHONY: map
 map:
@@ -351,12 +351,12 @@ test_flags = --verbosity:0
 .PHONY: test_charset
 test_charset: test/charset/run.sh $(OBJDIR)/chagashi_test
 	(cd test/charset && ./run.sh)
-	$(NIM) r $(test_flags) test/charset/basic.nim
-	CGS_TESTDIR=$(OBJDIR)/chagashi_test $(NIM) r $(test_flags) test/charset/data.nim
+	$(NIM) r $(test_flags) --nimcache:"$(OBJDIR)/test_charset" test/charset/basic.nim
+	CGS_TESTDIR=$(OBJDIR)/chagashi_test $(NIM) r --nimcache:"$(OBJDIR)/test_charset_data" $(test_flags) test/charset/data.nim
 
 .PHONY: test_nim
 test_nim: test/nim/ttwtstr.nim
-	(cd test/nim && $(NIM) r $(test_flags) ttwtstr.nim)
+	(cd test/nim && $(NIM) r --nimcache:"$(OBJDIR)/test_twtstr" $(test_flags) ttwtstr.nim)
 
 .PHONY: test
 test: test_js test_layout test_net test_md test_pager test_charset test_nim