cargo test fails for runtime-c-api at least on linux

[ethanfrey]

Describe the bug

Discovered when I updated versions while reporting #811
This is a minor typo that at least makes my ubuntu/linux c compiler complain.

echo "`wasmer -V` | `rustc -V` | `uname -m`"

wasmer: command not found
 | rustc 1.38.0-nightly (c43d03a19 2019-08-14) | x86_64

git log -1 provides:

commit 0ea5b1b2bd87a704e2963bb92b9c0d96e2bf66ba (HEAD -> master, origin/staging, origin/master)
Merge: 174cc9f0 71b865aa
Author: bors[bot] <26634292+bors[bot]@users.noreply.github.com>
Date:   Wed Sep 18 16:59:37 2019 +0000

Steps to reproduce

git checkout master
cd lib/runtime-c-api
cargo test

Expected behavior

Actual behavior

CMakeFiles/test-exports.dir/build.make:62: recipe for target 'CMakeFiles/test-exports.dir/test-exports.c.o' failed
CMakeFiles/Makefile2:289: recipe for target 'CMakeFiles/test-exports.dir/all' failed
Makefile:94: recipe for target 'all' failed

stderr:
/home/ethan/IdeaProjects/wasmer/lib/runtime-c-api/tests/test-exports.c: In function ‘main’:
/home/ethan/IdeaProjects/wasmer/lib/runtime-c-api/tests/test-exports.c:245:28: error: format ‘%lld’ expects argument of type ‘long long int’, but argument 2 has type ‘int64_t {aka long int}’ [-Werror=format=]
         printf("Result: %lld\n", outputs[0].value.I64);
                         ~~~^     ~~~~~~~~~~~~~~~~~~~~
                         %ld
cc1: all warnings being treated as errors
make[2]: *** [CMakeFiles/test-exports.dir/test-exports.c.o] Error 1
make[1]: *** [CMakeFiles/test-exports.dir/all] Error 2
make: *** [all] Error 2

Additional context

[Hywan]

Thank you for the bug report!