Fix no_core and no_std rustdoc tests on Windows

This prevents the following (very strange) errors:

```
error: linking with `link.exe` failed: exit code: 1120
  |
  = note: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise\\VC\\Tools\\MSVC\\14.29.30133\\bin\\HostX64\\x86\\link.exe" "/DEF:C:\\Users\\runneradmin\\AppData\\Local\\Temp\\rustcJih4fa\\lib.def" "/NOLOGO" "/LARGEADDRESSAWARE" "/SAFESEH" "D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\test\\rustdoc\\issue-15318-2\\auxiliary\\issue-15318.issue_15318.0a2a8554-cgu.0.rcgu.o" "D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\test\\rustdoc\\issue-15318-2\\auxiliary\\issue-15318.1na9aylmt25n6w3f.rcgu.o" "/LIBPATH:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\native\\rust-test-helpers" "/LIBPATH:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\test\\rustdoc\\issue-15318-2\\auxiliary" "/LIBPATH:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\i686-pc-windows-msvc\\lib" "vcruntime.lib" "ucrt.lib" "/WHOLEARCHIVE:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\i686-pc-windows-msvc\\lib\\librustc_std_workspace_core-78744e1360284b1e.rlib" "/WHOLEARCHIVE:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\i686-pc-windows-msvc\\lib\\libcore-a900fa3d16956226.rlib" "D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\i686-pc-windows-msvc\\lib\\libcompiler_builtins-eb97e6b4dfd2f421.rlib" "/NXCOMPAT" "/LIBPATH:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\i686-pc-windows-msvc\\lib" "/OUT:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\test\\rustdoc\\issue-15318-2\\auxiliary\\issue_15318.dll" "/OPT:REF,ICF" "/DLL" "/IMPLIB:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\test\\rustdoc\\issue-15318-2\\auxiliary\\issue_15318.dll.lib" "/DEBUG" "/NATVIS:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\etc\\intrinsic.natvis" "/NATVIS:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\etc\\liballoc.natvis" "/NATVIS:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\etc\\libcore.natvis" "/NATVIS:D:\\a\\rust\\rust\\build\\i686-pc-windows-msvc\\stage2\\lib\\rustlib\\etc\\libstd.natvis"
  = note: LINK : warning LNK4216: Exported entry point __DllMainCRTStartup@12
             Creating library D:\a\rust\rust\build\i686-pc-windows-msvc\test\rustdoc\issue-15318-2\auxiliary\issue_15318.dll.lib and object D:\a\rust\rust\build\i686-pc-windows-msvc\test\rustdoc\issue-15318-2\auxiliary\issue_15318.dll.exp
          libcore-a900fa3d16956226.rlib(core-a900fa3d16956226.core.95dedc69-cgu.0.rcgu.o) : error LNK2019: unresolved external symbol __aulldiv referenced in function __ZN4core3num7dec2flt7decimal7Decimal10left_shift17hfb9b6c23d6ff0383E
          libcompiler_builtins-eb97e6b4dfd2f421.rlib(compiler_builtins-eb97e6b4dfd2f421.compiler_builtins.a5ef280a-cgu.51.rcgu.o) : error LNK2001: unresolved external symbol __aulldiv
          libcore-a900fa3d16956226.rlib(core-a900fa3d16956226.core.95dedc69-cgu.0.rcgu.o) : error LNK2019: unresolved external symbol __aullrem referenced in function __ZN4core3fmt3num14parse_u64_into17h90eb20517ec3bd86E
          D:\a\rust\rust\build\i686-pc-windows-msvc\test\rustdoc\issue-15318-2\auxiliary\issue_15318.dll : fatal error LNK1120: 2 unresolved externals

```

src/test/rustdoc/auxiliary/issue-15318.rs

@@ -1,5 +1,6 @@
+// no-prefer-dynamic
 // compile-flags: -Cmetadata=aux
-
+#![crate_type = "rlib"]
 #![doc(html_root_url = "http://example.com/")]
 #![feature(lang_items)]
 #![no_std]

src/test/rustdoc/cross-crate-primitive-doc.rs

@@ -1,5 +1,7 @@
 // aux-build:primitive-doc.rs
 // compile-flags: --extern-html-root-url=primitive_doc=../ -Z unstable-options
+// ignore-windows
+
 #![feature(no_core)]
 #![no_core]