Make improvements

- Introduce portable sched_getcpu() api
- Support GCC's __target_clones__ feature
- Make fma() go faster on x86 in default mode
- Remove some asan checks from core libraries
- WinMain() now ensures $HOME and $USER are defined

third_party/compiler_rt/cpu_model.h

@@ -0,0 +1,33 @@
+//===-- cpu_model_common.c - Utilities for cpu model detection ----*- C -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements common utilities for runtime cpu model detection.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef COMPILER_RT_LIB_BUILTINS_CPU_MODEL_COMMON_H
+#define COMPILER_RT_LIB_BUILTINS_CPU_MODEL_COMMON_H
+
+#if __has_attribute(constructor)
+#if __GNUC__ >= 9
+// Ordinarily init priorities below 101 are disallowed as they are reserved for
+// the implementation. However, we are the implementation, so silence the
+// diagnostic, since it doesn't apply to us.
+#pragma GCC diagnostic ignored "-Wprio-ctor-dtor"
+#endif
+// We're choosing init priority 90 to force our constructors to run before any
+// constructors in the end user application (starting at priority 101). This
+// value matches the libgcc choice for the same functions.
+#define CONSTRUCTOR_ATTRIBUTE __attribute__((__constructor__(90)))
+#else
+// FIXME: For MSVC, we should make a function pointer global in .CRT$X?? so that
+// this runs during initialization.
+#define CONSTRUCTOR_ATTRIBUTE
+#endif
+
+#endif