[Fix Master] Fix coverage between go/cpp code

Summary:
This is currently breaking master, likely because of the Go 1.13 upgrade. With this upgrade it
seems that we need to explicitly pass in gcov flags.

Test Plan: bazel test //... and bazel coverage //src/...

Reviewers: oazizi, philkuz, #engineering

Reviewed By: oazizi, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D1916

GitOrigin-RevId: 83631e5bf6c51fdc78e6068f42635ee05991c4ba

.bazelrc

@@ -86,6 +86,7 @@ build --cxxopt -std=c++17
 coverage --cxxopt -fprofile-arcs
 coverage --cxxopt -ftest-coverage
 coverage --instrument_test_targets
+coverage --define PL_COVERAGE=true
 
 # Use stable GIT build tag by default.
 build --define BUNDLE_VERSION={STABLE_BUILD_TAG}

bazel/BUILD.bazel

@@ -9,3 +9,11 @@ config_setting(
     name = "debug_tcmalloc",
     values = {"define": "tcmalloc=debug"},
 )
+
+config_setting(
+    name = "coverage_enabled",
+    values = {
+        "define": "PL_COVERAGE=true",
+    },
+    visibility = ["//visibility:public"],
+)

bazel/pl_build_system.bzl

@@ -251,7 +251,10 @@ def tcmalloc_external_deps(repository):
 
 def pl_cgo_library(**kwargs):
     if "cgo" in kwargs and kwargs["cgo"] and "clinkopts" not in kwargs:
-        kwargs["clinkopts"] = pl_linkopts()
+        kwargs["clinkopts"] = pl_linkopts() + select({
+            "@pl//bazel:coverage_enabled": ["-lgcov --coverage"],
+            "//conditions:default": [],
+        })
         kwargs["toolchains"] = ["@bazel_tools//tools/cpp:current_cc_toolchain"]
     go_library(**kwargs)