target: Implement OS version detection for Windows

lib/std/os/windows/bits.zig

@@ -1321,3 +1321,16 @@ pub const PSAPI_WS_WATCH_INFORMATION_EX = extern struct {
     Flags: ULONG_PTR,
 };
 pub const PPSAPI_WS_WATCH_INFORMATION_EX = *PSAPI_WS_WATCH_INFORMATION_EX;
+
+pub const OSVERSIONINFOW = extern struct {
+    dwOSVersionInfoSize: ULONG,
+    dwMajorVersion: ULONG,
+    dwMinorVersion: ULONG,
+    dwBuildNumber: ULONG,
+    dwPlatformId: ULONG,
+    szCSDVersion: [128]WCHAR,
+};
+pub const POSVERSIONINFOW = *OSVERSIONINFOW;
+pub const LPOSVERSIONINFOW = *OSVERSIONINFOW;
+pub const RTL_OSVERSIONINFOW = OSVERSIONINFOW;
+pub const PRTL_OSVERSIONINFOW = *RTL_OSVERSIONINFOW;

lib/std/os/windows/ntdll.zig

@@ -1,6 +1,14 @@
 usingnamespace @import("bits.zig");
 
-pub extern "NtDll" fn RtlCaptureStackBackTrace(FramesToSkip: DWORD, FramesToCapture: DWORD, BackTrace: **c_void, BackTraceHash: ?*DWORD) callconv(.Stdcall) WORD;
+pub extern "NtDll" fn RtlGetVersion(
+    lpVersionInformation: PRTL_OSVERSIONINFOW,
+) callconv(.Stdcall) NTSTATUS;
+pub extern "NtDll" fn RtlCaptureStackBackTrace(
+    FramesToSkip: DWORD,
+    FramesToCapture: DWORD,
+    BackTrace: **c_void,
+    BackTraceHash: ?*DWORD,
+) callconv(.Stdcall) WORD;
 pub extern "NtDll" fn NtQueryInformationFile(
     FileHandle: HANDLE,
     IoStatusBlock: *IO_STATUS_BLOCK,

lib/std/zig/system.zig

@@ -221,7 +221,44 @@ pub const NativeTargetInfo = struct {
                     }
                 },
                 .windows => {
-                    // TODO Detect native operating system version.
+                    var version_info: std.os.windows.RTL_OSVERSIONINFOW = undefined;
+                    version_info.dwOSVersionInfoSize = @sizeOf(@TypeOf(version_info));
+
+                    switch (std.os.windows.ntdll.RtlGetVersion(&version_info)) {
+                        .SUCCESS => {},
+                        else => unreachable,
+                    }
+
+                    // Starting from the system infos build a NTDDI-like version
+                    // constant whose format is:
+                    //   B0 B1 B2 B3
+                    //   `---` `` ``--> Sub-version (Starting from Windows 10 onwards)
+                    //     \    `--> Service pack (Always zero in the constants defined)
+                    //      `--> OS version (Major & minor)
+                    const os_ver: u16 = //
+                        @intCast(u16, version_info.dwMajorVersion & 0xff) << 8 |
+                        @intCast(u16, version_info.dwMinorVersion & 0xff);
+                    const sp_ver: u8 = 0;
+                    const sub_ver: u8 = if (os_ver >= 0x0A00) subver: {
+                        // There's no other way to obtain this info beside
+                        // checking the build number against a known set of
+                        // values
+                        const known_build_numbers = [_]u32{
+                            10240, 10586, 14393, 15063, 16299, 17134, 17763,
+                            18362, 18363,
+                        };
+                        var last_idx: usize = 0;
+                        for (known_build_numbers) |build, i| {
+                            if (version_info.dwBuildNumber >= build)
+                                last_idx = i;
+                        }
+                        break :subver @truncate(u8, last_idx);
+                    } else 0;
+
+                    const version: u32 = @as(u32, os_ver) << 16 | @as(u32, sp_ver) << 8 | sub_ver;
+
+                    os.version_range.windows.max = @intToEnum(Target.Os.WindowsVersion, version);
+                    os.version_range.windows.min = @intToEnum(Target.Os.WindowsVersion, version);
                 },
                 .macosx => {
                     // TODO Detect native operating system version.