Add a Bazel build file for opentracing-cpp.

BUILD.bazel

@@ -0,0 +1,30 @@
+cc_library(
+    name = "opentracing",
+    srcs = glob(["src/*.cpp"]),
+    hdrs = glob(["include/opentracing/*.h"]) + [
+        ":include/opentracing/version.h",
+    ],
+    strip_include_prefix = "include",
+    visibility = ["//visibility:public"],
+    deps = [":3rd_party_lib"],
+)
+
+genrule(
+    name = "generate_version_h",
+    srcs = glob([
+        "*",
+        "cmake/*",
+        "src/*",
+    ]),
+    outs = ["include/opentracing/version.h"],
+    cmd = """
+    cmake -DBUILD_TESTING=OFF -L $$(dirname $(location :CMakeLists.txt))
+    mv include/opentracing/version.h $@
+    """,
+)
+
+cc_library(
+    name = "3rd_party_lib",
+    hdrs = glob(["3rd_party/include/**/*.hpp"]),
+    strip_include_prefix = "3rd_party/include",
+)

WORKSPACE

@@ -0,0 +1 @@
+workspace(name = "io_opentracing_cpp")

test/BUILD

@@ -0,0 +1,12 @@
+TEST_NAMES = [
+    "string_view_test",
+    "tracer_test",
+    "util_test",
+    "value_test",
+]
+
+[cc_test(
+    name = test_name,
+    srcs = [test_name + ".cpp"],
+    deps = ["//:opentracing"],
+) for test_name in TEST_NAMES]