fix: use printf instead of echo for portable \n handling in Makefile

echo's treatment of \n is shell-dependent (bash interprets it by
default, zsh and POSIX sh do not without -e). Switch report() and
the failure summary to printf in both integration-test and
test-skip-lang-start targets.

Author: cds-amal

Makefile

@@ -26,7 +26,7 @@ integration-test: NORMALIZE ?= jq -S -e -f $(TESTDIR)/../normalise-filter.jq
 integration-test: DIFF      ?= | diff -
 integration-test:
 	errors=""; \
-	report() { echo "$$1: $$2"; errors="$$errors\n$$1: $$2"; }; \
+	report() { printf "%s: %s\n" "$$1" "$$2"; errors="$$errors\n$$1: $$2"; }; \
 	for rust in ${TESTS}; do \
 		target=$${rust%.rs}.smir.json; \
 		dir=$$(dirname $${rust}); \
@@ -37,7 +37,7 @@ integration-test:
 			&& rm $${target} \
 			|| report "$$rust" "Unexpected json output"; \
 		done; \
-	[ -z "$$errors" ] || (echo "===============\nFAILING TESTS:$$errors"; exit 1)
+	[ -z "$$errors" ] || (printf "===============\nFAILING TESTS:%s\n" "$$errors"; exit 1)
 
 
 golden:
@@ -48,7 +48,7 @@ test-skip-lang-start: TESTS ?= $(shell find $(TESTDIR) -type f -name "*.rs")
 test-skip-lang-start: SMIR  ?= cargo run -- --d2 "-Zno-codegen"
 test-skip-lang-start:
 	errors=""; \
-	report() { echo "FAIL: $$1: $$2"; errors="$$errors\n$$1: $$2"; }; \
+	report() { printf "FAIL: %s: %s\n" "$$1" "$$2"; errors="$$errors\n$$1: $$2"; }; \
 	for rust in ${TESTS}; do \
 		dir=$$(dirname $${rust}); \
 		name=$$(basename $${rust} .rs); \
@@ -58,7 +58,7 @@ test-skip-lang-start:
 			|| { report "$$rust" "Conversion failed"; continue; }; \
 		rm -f $${d2}; \
 	done; \
-	[ -z "$$errors" ] || (echo "===============\nFAILING TESTS:$$errors"; exit 1)
+	[ -z "$$errors" ] || (printf "===============\nFAILING TESTS:%s\n" "$$errors"; exit 1)
 
 format: 
 	cargo fmt