core: remove core_platform build option and remove Null.zig

build.zig

@@ -45,7 +45,6 @@ pub fn build(b: *std.Build) !void {
     const target = b.standardTargetOptions(.{});
 
     const sysgpu_backend = b.option(SysgpuBackend, "sysgpu_backend", "sysgpu API backend") orelse .default;
-    const core_platform = b.option(Platform, "core_platform", "mach core platform to use") orelse Platform.fromTarget(target.result);
 
     const build_examples = b.option(bool, "examples", "build/install examples specifically");
     const build_libs = b.option(bool, "libs", "build/install libraries specifically");
@@ -68,7 +67,6 @@ pub fn build(b: *std.Build) !void {
     build_options.addOption(bool, "want_sysaudio", want_sysaudio);
     build_options.addOption(bool, "want_sysgpu", want_sysgpu);
     build_options.addOption(SysgpuBackend, "sysgpu_backend", sysgpu_backend);
-    build_options.addOption(Platform, "core_platform", core_platform);
 
     var examples = [_]Example{
         .{ .name = "core-custom-entrypoint", .deps = &.{} },

src/Core.zig

@@ -420,12 +420,17 @@ pub fn detectBackendType(allocator: std.mem.Allocator) !gpu.BackendType {
     @panic("unknown MACH_GPU_BACKEND type");
 }
 
-const Platform = switch (build_options.core_platform) {
-    .wasm => @panic("TODO: support mach.Core WASM platform"),
+const Platform = switch (builtin.target.os.tag) {
+    .wasi => @panic("TODO: support mach.Core WASM platform"),
+    .ios => @panic("TODO: support mach.Core IOS platform"),
     .windows => @import("core/Windows.zig"),
-    .linux => @import("core/Linux.zig"),
-    .darwin => @import("core/Darwin.zig"),
-    .null => @import("core/Null.zig"),
+    .linux => blk: {
+        if (builtin.target.abi.isAndroid())
+            @panic("TODO: support mach.Core Android platform");
+        break :blk @import("core/Linux.zig");
+    },
+    .macos => @import("core/Darwin.zig"),
+    else => {},
 };
 
 pub const InputState = struct {