Add a test step to produce a minimal binary using libbpf.

This patch adds a test step to link a minimal program to libbpf library produced,
making sure that the library works.

travis-ci/managers/test_compile.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+set -euox pipefail
+
+CFLAGS=${CFLAGS:-}
+
+cat << EOF > main.c
+#include <bpf/libbpf.h>
+int main() {
+  return bpf_object__open(0) < 0;
+}
+EOF
+
+# static linking
+${CC:-cc} ${CFLAGS} -o main -I./install/usr/include main.c ./build/libbpf.a -lelf -lz