Always use Rust based intrinsics on Windows

The check inside compiler-rt file int_types.h to #define CRT_HAS_128BIT
looks like:

 #if (defined(__LP64__) || defined(__wasm__)) && \
     !(defined(__mips__) && defined(__clang__))
 #define CRT_HAS_128BIT
 #endif

Windows uses LLP64 instead of LP64, so it doesn't ship with the C based
intrinsics.

Also, add libcompiler_builtins to the list of crates that may have platform
specific checks (like the ones we just added).

src/libcompiler_builtins/lib.rs

@@ -17,14 +17,16 @@
 #![crate_name = "compiler_builtins"]
 #![crate_type = "rlib"]
 #![feature(staged_api)]
-#![cfg_attr(any(target_pointer_width="32", target_pointer_width="16"),
+#![cfg_attr(any(target_pointer_width="32", target_pointer_width="16", target_os="windows",
+            target_arch="mips64"),
             feature(core_intrinsics, core_float))]
 #![feature(associated_consts)]
 #![cfg_attr(not(stage0), feature(i128_type))]
 
 #![allow(non_camel_case_types, unused_variables)]
 
-#[cfg(any(target_pointer_width="32", target_pointer_width="16"))]
+#[cfg(any(target_pointer_width="32", target_pointer_width="16", target_os="windows",
+          target_arch="mips64"))]
 pub mod reimpls {
 
     #![allow(unused_comparisons)]

src/tools/tidy/src/pal.rs

@@ -26,6 +26,7 @@
 //! exceptions:
 //!
 //! - core may not have platform-specific code
+//! - libcompiler_builtins may have platform-specific code
 //! - liballoc_system may have platform-specific code
 //! - liballoc_jemalloc may have platform-specific code
 //! - libpanic_abort may have platform-specific code
@@ -53,6 +54,7 @@ const EXCEPTION_PATHS: &'static [&'static str] = &[
     // std crates
     "src/liballoc_jemalloc",
     "src/liballoc_system",
+    "src/libcompiler_builtins",
     "src/liblibc",
     "src/libpanic_abort",
     "src/libpanic_unwind",