binman: Report an error if test files fail to compile

At present any error from the 'make' command is silently swallowed by the
test system. Fix this by showing it when detected.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/elf_test.py

@@ -70,8 +70,12 @@ def BuildElfTestFiles(target_dir):
     # correctly. So drop any make flags here.
     if 'MAKEFLAGS' in os.environ:
         del os.environ['MAKEFLAGS']
-    tools.Run('make', '-C', target_dir, '-f',
-              os.path.join(testdir, 'Makefile'), 'SRC=%s/' % testdir)
+    try:
+        tools.Run('make', '-C', target_dir, '-f',
+                  os.path.join(testdir, 'Makefile'), 'SRC=%s/' % testdir)
+    except ValueError as e:
+        # The test system seems to suppress this in a strange way
+        print(e)
 
 
 class TestElf(unittest.TestCase):