[zig ld] --gc-sections workaround + tests

`zig cc` emits `--gc-sections` for the linker, which is incompatbile
with what CGo thinks about linking.

This commit adds a workaround: it will add `--no-gc-sections` to the
linking step if the command is not specified (falling back to the
default behavior of gcc/clang).

Related: https://github.com/golang/go/issues/52690

test/cgo/BUILD

@@ -0,0 +1,52 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+load("//rules:rules_go.bzl", "go_binary")
+load("@bazel-zig-cc//rules:platform.bzl", "platform_binary", "platform_test")
+
+go_library(
+    name = "cgo_lib",
+    srcs = ["cgo.go"],
+    cgo = True,
+    importpath = "git.sr.ht/~motiejus/bazel-zig-cc/test/cgo",
+    visibility = ["//visibility:private"],
+)
+
+go_test(
+    name = "cgo_test",
+    srcs = ["cgo_test.go"],
+    embed = [":cgo_lib"],
+)
+
+go_binary(
+    name = "cgo",
+    embed = [":cgo_lib"],
+    visibility = ["//visibility:public"],
+)
+
+[
+    platform_binary(
+        name = "cgo_{}".format(name),
+        src = "cgo",
+        platform = platform,
+    )
+    for name, platform in [
+        ("linux_amd64_musl", "//libc_aware/platform:linux_amd64_musl"),
+        ("linux_amd64_gnu.2.19", "//libc_aware/platform:linux_amd64_gnu.2.19"),
+        ("linux_arm64_musl", "//libc_aware/platform:linux_arm64_musl"),
+        ("linux_arm64_gnu.2.28", "//libc_aware/platform:linux_arm64_gnu.2.28"),
+        ("darwin_amd64", "//platform:darwin_amd64"),
+    ]
+]
+
+[
+    platform_test(
+        name = "cgo_test_{}".format(name),
+        src = "cgo_test",
+        platform = platform,
+    )
+    for name, platform in [
+        ("linux_amd64_musl", "//libc_aware/platform:linux_amd64_musl"),
+        ("linux_amd64_gnu.2.19", "//libc_aware/platform:linux_amd64_gnu.2.19"),
+        ("linux_arm64_musl", "//libc_aware/platform:linux_arm64_musl"),
+        ("linux_arm64_gnu.2.28", "//libc_aware/platform:linux_arm64_gnu.2.28"),
+    ]
+]

test/cgo/cgo.go

@@ -0,0 +1,17 @@
+package main
+
+// #define _FILE_OFFSET_BITS 64
+// #include <unistd.h>
+// #include <fcntl.h>
+// #include <stdio.h>
+// char* hello() { return "hello, world"; }
+// void phello() { printf("%s, your lucky number is %p\n", hello(), fcntl); }
+import "C"
+
+func main() {
+	C.phello()
+}
+
+func Chello() string {
+	return C.GoString(C.hello())
+}

test/cgo/cgo_test.go

@@ -0,0 +1,13 @@
+package main
+
+import (
+	"testing"
+)
+
+func TestHello(t *testing.T) {
+	want := "hello, world"
+	got := Chello()
+	if got != want {
+		t.Errorf("expected %q, got %q", want, got)
+	}
+}