[builtins] Do not assume sizeof(long long)==8 in int_div_impl.inc

[bjope]

Summary

Got some regressions downstream after commit b541196eb45d80f2d
due to the new code assuming sizeof(long long)==8. This is a fixup
for that problem.

And while being at it, also adding the missing file header.

[bjope]

Update after feedback (check sizeof(long long) rather than using CHAR_BIT).

[bjope]

Use "unsigned long long" instead of "long long" to match __builtin_clzll.

[MaskRay]

Pushed 17772995d48b8c10a3142d602e228f3ebeed85bf instead

It is still unclear to me why assuming sizeof(long long)==8 can cause problems. You need to provide more information.

[bjope]

In D78300#1989021, @MaskRay wrote:

Pushed 17772995d48b8c10a3142d602e228f3ebeed85bf instead

It is still unclear to me why assuming sizeof(long long)==8 can cause problems. You need to provide more information.

udivdi3 use du_int, which maps to unsigned long long. And with CHAR_BIT=16 we get sizeof(du_int)==sizeof(unsigned long lon)==4.
For udivdi3.c (which is doing typedef du_int fixuint_t) we ended up using bultin_clz for the unsigned long long division, as the comparison was checking if sizeof(fixuint_t) was 8.

[bjope]

This was fixed in https://reviews.llvm.org/rG17772995d48b8c10a3142d602e228f3ebeed85bf

compiler-rt/lib/builtins/int_div_impl.inc

-#define clz(a) (sizeof(a) == 8 ? __builtin_clzll(a) : __builtin_clz(a))
+//===----- int_div_impl.inc - integer division --------------------*- 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 helpers for udivXi3 and umodXi3.
+//
+//===----------------------------------------------------------------------===//
+
+#define clz(a) (sizeof(a) == sizeof(unsigned long long) ? __builtin_clzll(a) : __builtin_clz(a))
 
 // Adapted from Figure 3-40 of The PowerPC Compiler Writer's Guide
 static __inline fixuint_t __udivXi3(fixuint_t n, fixuint_t d) {
   const unsigned N = sizeof(fixuint_t) * CHAR_BIT;
   // d == 0 cases are unspecified.
   unsigned sr = (d ? clz(d) : N) - (n ? clz(n) : N);
   // 0 <= sr <= N - 1 or sr is very large.
   if (sr > N - 1) // n < d