move -j1 setting to BUILDEROPTIONS, set in debian/rules file

I needed BUILDEROPTIONS to allow passing flags to stack build, but it also
lets me move the -j1 out of the normal build path, and to debian/rules
which has the goal of having a reproducible build

Makefile

@@ -18,14 +18,13 @@ build: $(all)
 Build/SysConfig.hs: configure.hs Build/TestConfig.hs Build/Configure.hs
 	if [ "$(BUILDER)" = ./Setup ]; then ghc --make Setup; fi
 	if [ "$(BUILDER)" = stack ]; then \
-		$(BUILDER) build -j1; \
+		$(BUILDER) build $(BUILDEROPTIONS); \
 	else \
 		$(BUILDER) configure --ghc-options="$(shell Build/collect-ghc-options.sh)"; \
 	fi
 
-# -j1 is used for reproducible build
 git-annex: Build/SysConfig.hs
-	$(BUILDER) build -j1
+	$(BUILDER) build $(BUILDEROPTIONS)
 	if [ "$(BUILDER)" = stack ]; then \
 		ln -sf $$(find .stack-work/ -name git-annex -type f | grep build/git-annex/git-annex | tail -n 1) git-annex; \
 	else \

debian/rules

@@ -2,6 +2,9 @@
 
 export BUILDER=debian/cabal-wrapper
 
+# -j1 is used for reproducible build
+export BUILDEROPTIONS=-j1
+
 STANDALONE_BUILD=$(shell grep -qe '^Package: git-annex-standalone' debian/control \
                          && echo 1 || echo 0)