[libc] Fix UBSan error after D147171

libc/src/__support/CMakeLists.txt

add_header_library(
   str_to_integer
   HDRS
     str_to_integer.h
   DEPENDS
     .ctype_utils
     .str_to_num_result
     libc.src.errno.errno
     libc.src.__support.CPP.limits
+    libc.src.__support.CPP.type_traits
     libc.src.__support.common
 )
 
 add_header_library(
   integer_to_string
   HDRS
     integer_to_string.h
   DEPENDS

libc/src/__support/str_to_integer.h

 //===-- String to integer conversion utils ----------------------*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LIBC_SRC_SUPPORT_STR_TO_INTEGER_H
 #define LIBC_SRC_SUPPORT_STR_TO_INTEGER_H
 
 #include "src/__support/CPP/limits.h"
+#include "src/__support/CPP/type_traits.h"
 #include "src/__support/common.h"
 #include "src/__support/ctype_utils.h"
 #include "src/__support/str_to_num_result.h"
 #include "src/errno/libc_errno.h" // For ERANGE
 #include <limits.h>
 
 namespace __llvm_libc {
 namespace internal {
LIBC_INLINE StrToNumResult<T> strtointeger(const char *__restrict src,
 
   if (error_val == ERANGE) {
     if (is_positive || IS_UNSIGNED)
       return {cpp::numeric_limits<T>::max(), str_len, error_val};
     else // T is signed and there is a negative overflow
       return {cpp::numeric_limits<T>::min(), str_len, error_val};
   }
 
-  return {is_positive ? static_cast<T>(result) : -static_cast<T>(result),
+  return {is_positive
+              ? static_cast<T>(result)
+              : static_cast<T>(-static_cast<cpp::make_unsigned_t<T>>(result)),
           str_len, error_val};
 }
 
 } // namespace internal
 } // namespace __llvm_libc
 
 #endif // LIBC_SRC_SUPPORT_STR_TO_INTEGER_H