Add constant-time test to make check and make Travis fail if it fails

Moreover, this changes the way Travis runs the constant-time tests
by adding a `--error-exitcode=1` parameter to valgrind. Without that
parameter, valgrind simply passes the exit code through, even in the
case of valgrind errors. That is, Travis would succeed even if
valgrind found problems.

.gitignore

@@ -31,6 +31,8 @@ libtool
 *.lo
 *.o
 *~
+*.log
+*.trs
 src/libsecp256k1-config.h
 src/libsecp256k1-config.h.in
 src/ecmult_static_context.h

.travis.yml

@@ -95,7 +95,7 @@ script:
    travis_wait 30 valgrind --error-exitcode=42 ./exhaustive_tests;
    fi
  - if [ -n "$CTIMETEST" ]; then
-   libtool --mode=execute valgrind  ./valgrind_ctime_test &> valgrind_ctime_test.log;
+   ./valgrind_ctime_test.sh &> valgrind_ctime_test.log;
    fi
 
 after_script:

Makefile.am

@@ -96,6 +96,7 @@ tests_CPPFLAGS = -DSECP256K1_BUILD -I$(top_srcdir)/src -I$(top_srcdir)/include $
 if VALGRIND_ENABLED
 tests_CPPFLAGS += -DVALGRIND
 noinst_PROGRAMS += valgrind_ctime_test
+TESTS += valgrind_ctime_test.sh
 valgrind_ctime_test_SOURCES = src/valgrind_ctime_test.c
 valgrind_ctime_test_LDADD = libsecp256k1.la $(SECP_LIBS) $(SECP_TEST_LIBS) $(COMMON_LIB)
 endif
@@ -141,7 +142,7 @@ src/ecmult_static_context.h: $(gen_context_BIN)
 CLEANFILES = $(gen_context_BIN) src/ecmult_static_context.h
 endif
 
-EXTRA_DIST = autogen.sh src/gen_context.c src/basic-config.h
+EXTRA_DIST = autogen.sh valgrind_ctime_test.sh src/gen_context.c src/basic-config.h
 
 if ENABLE_MODULE_ECDH
 include src/modules/ecdh/Makefile.am.include

src/valgrind_ctime_test.c

@@ -28,7 +28,7 @@ int main(void) {
     if (!RUNNING_ON_VALGRIND) {
         fprintf(stderr, "This test can only usefully be run inside valgrind.\n");
         fprintf(stderr, "Usage: libtool --mode=execute valgrind ./valgrind_ctime_test\n");
-        exit(1);
+        exit(99); /* indicates "ERROR" in make check */
     }
 
     /** In theory, testing with a single secret input should be sufficient:

valgrind_ctime_test.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+libtool --mode=execute valgrind --error-exitcode=1 ./valgrind_ctime_test "$@"
+
+case $? in
+    127) # "command not found", i.e., either libtool or valgrind not installed
+        exit 77 # map this to "SKIP" (=77) for make check
+        ;;
+    *)
+        exit $?
+        ;;
+esac