'make test': show failing test cases when cmake does

When building with make, `make test` runs `run-test-suites.pl` which has a
verbose mode that reports the failing test cases, but it didn't provide a
way to enable this verbose mode. With the present commit, you can run `make
test TEST_FLAGS=-v` to use verbose mode.

Base the default for verbose mode on the same environment variable that
`make test` uses when building with CMake: default off, but enabled if
`CTEST_OUTPUT_ON_FAILURE` is true. In particular, verbose mode will now be
on when building from `all.sh`.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/Makefile b/tests/Makefile
index 449fca2..db642c7 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -5,6 +5,9 @@
 WARNING_CFLAGS ?= -Wall -Wextra -Wformat=2 -Wno-format-nonliteral
 LDFLAGS ?=
 
+# Set this to -v to see the details of failing test cases
+TEST_FLAGS ?= $(if $(filter-out 0 OFF Off off NO No no FALSE False false N n,$(CTEST_OUTPUT_ON_FAILURE)),-v,)
+
 default: all
 
 # Include public header files from ../include, test-specific header files
@@ -195,7 +198,7 @@
 
 # Test suites caught by SKIP_TEST_SUITES are built but not executed.
 check: $(BINARIES)
-	perl scripts/run-test-suites.pl --skip=$(SKIP_TEST_SUITES)
+	perl scripts/run-test-suites.pl $(TEST_FLAGS) --skip=$(SKIP_TEST_SUITES)
 
 test: check
 
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 9944a85..583743c 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -178,7 +178,7 @@
         export MAKEFLAGS="-j"
     fi
 
-    # Include more verbose output for failing tests run by CMake
+    # Include more verbose output for failing tests run by CMake or make
     export CTEST_OUTPUT_ON_FAILURE=1
 
     # CFLAGS and LDFLAGS for Asan builds that don't use CMake