t/Makefile: make "check-meson" work with Dash

The "check-meson" target uses process substitution to check whether
extracted contents from "meson.build" match expected contents. Process
substitution is unportable though and thus the target will fail when
using for example Dash.

Fix this by writing data into a temporary directory.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/.gitignore

@@ -2,4 +2,5 @@
 /test-results
 /.prove
 /chainlinttmp
+/mesontmp
 /out/

t/Makefile

@@ -103,6 +103,7 @@ clean-except-prove-cache: clean-chainlint
 
 clean: clean-except-prove-cache
 	$(RM) -r '$(TEST_RESULTS_DIRECTORY_SQ)'
+	$(RM) -r mesontmp
 	$(RM) .prove
 
 clean-chainlint:
@@ -116,16 +117,17 @@ check-chainlint:
 
 check-meson:
 	@# awk acts up when trying to match single quotes, so we use \047 instead.
-	@printf "%s\n" \
+	@mkdir -p mesontmp && \
+	printf "%s\n" \
 		"integration_tests t[0-9][0-9][0-9][0-9]-*.sh" \
 		"unit_test_programs unit-tests/t-*.c" \
 		"clar_test_suites unit-tests/u-*.c" | \
 	while read -r variable pattern; do \
-		meson_tests=$$(awk "/^$$variable = \[\$$/ {flag=1 ; next } /^]$$/ { flag=0 } flag { gsub(/^  \047/, \"\"); gsub(/\047,\$$/, \"\"); print }" meson.build) && \
-		actual_tests=$$(ls $$pattern) && \
-		if test "$$meson_tests" != "$$actual_tests"; then \
+		awk "/^$$variable = \[\$$/ {flag=1 ; next } /^]$$/ { flag=0 } flag { gsub(/^  \047/, \"\"); gsub(/\047,\$$/, \"\"); print }" meson.build >mesontmp/meson.txt && \
+		ls $$pattern >mesontmp/actual.txt && \
+		if ! cmp mesontmp/meson.txt mesontmp/actual.txt; then \
 			echo "Meson tests differ from actual tests:"; \
-			diff -u <(echo "$$meson_tests") <(echo "$$actual_tests"); \
+			diff -u mesontmp/meson.txt mesontmp/actual.txt; \
 			exit 1; \
 		fi; \
 	done