windows: use ProcessPrng from bcryptprimitives.dll

rather than SystemFunction036 from advapi32. This has the advantage that
the code is loaded preemptively, preventing random numbers from
failing when they are needed for the first time on a system under heavy
load.

lib/std/os/windows.zig

@@ -22,6 +22,7 @@ test {
 }
 
 pub const advapi32 = @import("windows/advapi32.zig");
+pub const bcryptprimitives = @import("windows/bcryptprimitives.zig");
 pub const kernel32 = @import("windows/kernel32.zig");
 pub const ntdll = @import("windows/ntdll.zig");
 pub const ws2_32 = @import("windows/ws2_32.zig");
@@ -2644,33 +2645,6 @@ pub fn SetHandleInformation(h: HANDLE, mask: DWORD, flags: DWORD) SetHandleInfor
     }
 }
 
-pub const RtlGenRandomError = error{
-    /// `RtlGenRandom` has been known to fail in situations where the system is under heavy load.
-    /// Unfortunately, it does not call `SetLastError`, so it is not possible to get more specific
-    /// error information; it could actually be due to an out-of-memory condition, for example.
-    SystemResources,
-};
-
-/// Call RtlGenRandom() instead of CryptGetRandom() on Windows
-/// https://github.com/rust-lang-nursery/rand/issues/111
-/// https://bugzilla.mozilla.org/show_bug.cgi?id=504270
-pub fn RtlGenRandom(output: []u8) RtlGenRandomError!void {
-    var total_read: usize = 0;
-    var buff: []u8 = output[0..];
-    const max_read_size: ULONG = maxInt(ULONG);
-
-    while (total_read < output.len) {
-        const to_read: ULONG = @min(buff.len, max_read_size);
-
-        if (advapi32.RtlGenRandom(buff.ptr, to_read) == 0) {
-            return error.SystemResources;
-        }
-
-        total_read += to_read;
-        buff = buff[to_read..];
-    }
-}
-
 pub const WaitForSingleObjectError = error{
     WaitAbandoned,
     WaitTimeOut,

lib/std/os/windows/advapi32.zig

@@ -28,11 +28,6 @@ pub extern "advapi32" fn RegQueryValueExW(
 
 pub extern "advapi32" fn RegCloseKey(hKey: HKEY) callconv(.winapi) LSTATUS;
 
-// RtlGenRandom is known as SystemFunction036 under advapi32
-// http://msdn.microsoft.com/en-us/library/windows/desktop/aa387694.aspx */
-pub extern "advapi32" fn SystemFunction036(output: [*]u8, length: ULONG) callconv(.winapi) BOOL;
-pub const RtlGenRandom = SystemFunction036;
-
 pub const RRF = struct {
     pub const RT_ANY: DWORD = 0x0000ffff;
 

lib/std/os/windows/bcryptprimitives.zig

@@ -0,0 +1,4 @@
+const std = @import("../../std.zig");
+const windows = std.os.windows;
+
+pub extern "bcryptprimitives" fn ProcessPrng(pbData: [*]u8, cbData: usize) callconv(.winapi) c_int;

lib/std/posix.zig

@@ -370,7 +370,7 @@ pub const GetRandomError = OpenError;
 /// library implementation.
 pub fn getrandom(buffer: []u8) GetRandomError!void {
     if (native_os == .windows) {
-        return windows.RtlGenRandom(buffer);
+        return assert(windows.bcryptprimitives.ProcessPrng(buffer.ptr, buffer.len) == 1);
     }
     if (builtin.link_libc and @TypeOf(system.arc4random_buf) != void) {
         system.arc4random_buf(buffer.ptr, buffer.len);

test/standalone/issue_5825/build.zig

@@ -32,7 +32,6 @@ pub fn build(b: *std.Build) void {
         }),
     });
     exe.subsystem = .console;
-    exe.root_module.linkSystemLibrary("advapi32", .{}); // for RtlGenRandom
     exe.root_module.linkSystemLibrary("kernel32", .{});
     exe.root_module.linkSystemLibrary("ntdll", .{});
     exe.root_module.addObject(obj);

test/standalone/test_obj_link_run/build.zig

@@ -12,7 +12,6 @@ pub fn build(b: *std.Build) void {
         test_obj.root_module.linkSystemLibrary("ntdll", .{});
         test_obj.root_module.linkSystemLibrary("kernel32", .{});
         test_obj.root_module.linkSystemLibrary("ws2_32", .{});
-        test_obj.root_module.linkSystemLibrary("advapi32", .{}); // for RtlGenRandom
     }
 
     const test_exe_mod = b.createModule(.{

test/standalone/windows_argv/build.zig

@@ -86,7 +86,6 @@ pub fn build(b: *std.Build) !void {
                 .optimize = optimize,
             }),
         });
-        lib_msvc.root_module.linkSystemLibrary("advapi32", .{}); // for RtlGenRandom
         const verify_msvc = b.addExecutable(.{
             .name = "verify-msvc",
             .root_module = b.createModule(.{