Makefile.proof: Allow to override $(jobs) for `proof-allconfigs`

Change-Id: I13397d67d5f5f0860c693948b3008e9d64fc0a8e
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/libhwbase/+/474
Tested-by: Ada SPARK <gnatbot@sourcearcade.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/Makefile.proof b/Makefile.proof
index 0332323..931c165 100644
--- a/Makefile.proof
+++ b/Makefile.proof
@@ -97,12 +97,13 @@
 allconfigs = $(wildcard configs/*)
 allconfigs-targets = $(addprefix allconfigs-,$(notdir $(allconfigs)))
 
+$(allconfigs-targets): jobs=1
 $(allconfigs-targets): allconfigs-%: configs/%
 	rm -rf proof-allconfigs/$* $(name)_$*.gpr
 	mkdir -p proof-allconfigs/$*
 	echo "$(PROOF_MODE)" >proof-allconfigs/$*/proofmode
 	$(call filter-output, \
-	  $(MAKE) obj=proof-allconfigs/$* cnf=configs/$* gpr=$(name)_$*.gpr jobs=1 \
+	  $(MAKE) obj=proof-allconfigs/$* cnf=configs/$* gpr=$(name)_$*.gpr jobs=$(jobs) \
 		  proof-allconfigs/$*/gnatprove/gnatprove.out, \
 	  sed 's/^[^[:space:]]\+:[0-9]\+:[0-9]\+:/$*::&/')