tests: add test for --strip-trailing-cr UMR bug

* tests/strip-trailing-cr: New file. Test for today's bug fix.
* tests/Makefile.am (TESTS): Add it.

tests/Makefile.am

@@ -21,6 +21,7 @@ TESTS = \
   stdin \
   strcoll-0-names \
   filename-quoting \
+  strip-trailing-cr \
   colors
 
 XFAIL_TESTS = large-subopt

tests/strip-trailing-cr

@@ -0,0 +1,20 @@
+#!/bin/sh
+# Before diff-3.7, this would provoke a UMR
+
+. "${srcdir=.}/init.sh"; path_prepend_ ../src
+
+fail=0
+
+require_valgrind_
+
+printf '\r' > r || framework_failure_
+echo b > b || framework_failure_
+
+for opt in '' u c Dfoo; do
+  returns_ 1 valgrind --quiet --error-exitcode=3 \
+    diff -a$opt --strip-trailing-cr r b > out 2> err || fail=1
+done
+
+compare /dev/null err || fail=1
+
+Exit $fail