Add Zig build system

.gitignore

@@ -160,3 +160,5 @@ test/default/verify1
 test/default/xchacha20
 test/js.done
 testing
+zig-cache
+zig-out

build.zig

@@ -0,0 +1,88 @@
+const std = @import("std");
+const builtin = @import("builtin");
+const fmt = std.fmt;
+const fs = std.fs;
+const heap = std.heap;
+const mem = std.mem;
+const LibExeObjStep = std.build.LibExeObjStep;
+
+pub fn build(b: *std.build.Builder) !void {
+    const src_path = "src/libsodium";
+    const src_dir = try fs.Dir.openDir(fs.cwd(), src_path, .{ .iterate = true, .no_follow = true });
+
+    var target = b.standardTargetOptions(.{});
+    var mode = b.standardReleaseOptions();
+
+    const static = b.addStaticLibrary("sodium", null);
+    const shared = b.addSharedLibrary("sodium", null, .unversioned);
+    const libs = [_]*LibExeObjStep{ static, shared };
+
+    const prebuilt_version_file_path = "builds/msvc/version.h";
+    const version_file_path = "include/sodium/version.h";
+
+    if (src_dir.access(version_file_path, .{ .mode = .read_only })) {} else |_| {
+        try fs.cwd().copyFile(prebuilt_version_file_path, src_dir, version_file_path, .{});
+    }
+
+    for (libs) |lib| {
+        lib.setTarget(target);
+        lib.setBuildMode(mode);
+        lib.install();
+        if (mode != .Debug) {
+            lib.strip = true;
+        }
+        lib.linkLibC();
+
+        lib.addIncludeDir("src/libsodium/include/sodium");
+        lib.defineCMacro("CONFIGURED", "1");
+        lib.defineCMacro("DEV_MODE", "1");
+        lib.defineCMacro("_GNU_SOURCE", "1");
+        lib.defineCMacro("HAVE_INLINE_ASM", "1");
+        lib.defineCMacro("HAVE_TI_MODE", "1");
+        lib.defineCMacro("HAVE_ATOMIC_OPS", "1");
+
+        switch (target.getCpuArch()) {
+            .x86_64 => {
+                lib.defineCMacro("HAVE_AMD64_ASM", "1");
+                lib.defineCMacro("HAVE_AVX_ASM", "1");
+                lib.defineCMacro("HAVE_CPUID", "1");
+                lib.defineCMacro("HAVE_MMINTRIN_H", "1");
+                lib.defineCMacro("HAVE_EMMINTRIN_H", "1");
+                lib.defineCMacro("HAVE_PMMINTRIN_H", "1");
+            },
+            .aarch64, .aarch64_be => {
+                lib.defineCMacro("HAVE_ARMCRYTO", "1");
+            },
+            .wasm32, .wasm64 => {
+                lib.defineCMacro("__wasm__", "1");
+            },
+            else => {},
+        }
+
+        switch (target.getOsTag()) {
+            .wasi => {
+                lib.defineCMacro("__wasi__", "1");
+            },
+            else => {},
+        }
+
+        var allocator = heap.page_allocator;
+        var walker = try src_dir.walk(allocator);
+        while (try walker.next()) |entry| {
+            const name = entry.basename;
+            if (mem.endsWith(u8, name, ".c")) {
+                const full_path = try fmt.allocPrint(allocator, "{s}/{s}", .{ src_path, entry.path });
+                lib.addCSourceFiles(&.{full_path}, &.{
+                    "-fvisibility=hidden",
+                    "-fno-strict-aliasing",
+                    "-fno-strict-overflow",
+                    "-fwrapv",
+                    "-flax-vector-conversions",
+                });
+            } else if (mem.endsWith(u8, name, ".S")) {
+                const full_path = try fmt.allocPrint(allocator, "{s}/{s}", .{ src_path, entry.path });
+                lib.addAssemblyFile(full_path);
+            }
+        }
+    }
+}