[libc] Remove <functional> dependency in syscall_test.cpp

[abrachet]

Summary

Create self contained functional header which has a type similar to std::function

libc/test/config/linux/x86_64/syscall_test.cpp

 //===-- Unittests for x86_64 syscalls -------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "config/linux/syscall.h"
 #include "utils/UnitTest/Test.h"
 
-#include <functional>
+#include "utils/CPP/Functional.h"
 
 TEST(X86_64_SyscallTest, APITest) {
   // We only do a signature test here. Actual functionality tests are
   // done by the unit tests of the syscall wrappers like mmap.
 
-  std::function<long(long)> f([](long n) { return __llvm_libc::syscall(n); });
-  std::function<long(long, long)> f1(
+  using __llvm_libc::cpp::function;
+
+  function<long(long)> f([](long n) { return __llvm_libc::syscall(n); });
+  function<long(long, long)> f1(
       [](long n, long a1) { return __llvm_libc::syscall(n, a1); });
-  std::function<long(long, long, long)> f2(
+  function<long(long, long, long)> f2(
       [](long n, long a1, long a2) { return __llvm_libc::syscall(n, a1, a2); });
-  std::function<long(long, long, long, long)> f3(
+  function<long(long, long, long, long)> f3(
       [](long n, long a1, long a2, long a3) {
         return __llvm_libc::syscall(n, a1, a2, a3);
       });
-  std::function<long(long, long, long, long, long)> f4(
+  function<long(long, long, long, long, long)> f4(
       [](long n, long a1, long a2, long a3, long a4) {
         return __llvm_libc::syscall(n, a1, a2, a3, a4);
       });
-  std::function<long(long, long, long, long, long, long)> f5(
+  function<long(long, long, long, long, long, long)> f5(
       [](long n, long a1, long a2, long a3, long a4, long a5) {
         return __llvm_libc::syscall(n, a1, a2, a3, a4, a5);
       });
-  std::function<long(long, long, long, long, long, long, long)> f6(
+  function<long(long, long, long, long, long, long, long)> f6(
       [](long n, long a1, long a2, long a3, long a4, long a5, long a6) {
         return __llvm_libc::syscall(n, a1, a2, a3, a4, a5, a6);
       });
 
-  std::function<long(long, void *)> notLongType(
-      [](long n, void *a1) {
-        return __llvm_libc::syscall(n, a1);
-      });
+  function<long(long, void *)> notLongType(
+      [](long n, void *a1) { return __llvm_libc::syscall(n, a1); });
 }

libc/utils/CPP/CMakeLists.txt

 add_header_library(
   standalone_cpp
   HDRS
     Array.h
     ArrayRef.h
+    Functional.h
+    StringRef.h
     TypeTraits.h
 )

libc/utils/CPP/Functional.h

+//===-- Self contained functional header ------------------------*- 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 LLVM_LIBC_UTILS_CPP_FUNCTIONAL_H
+#define LLVM_LIBC_UTILS_CPP_FUNCTIONAL_H
+
+namespace __llvm_libc {
+namespace cpp {
+
+template <typename Func> class function;
+
+template <typename Ret, typename... Params> class function<Ret(Params...)> {
+  Ret (*func)(Params...) = nullptr;
+
+public:
+  constexpr function() = default;
+  template <typename Func> constexpr function(Func &&f) : func(f) {}
+
+  constexpr Ret operator()(Params... params) { return func(params...); }
+};
+
+} // namespace cpp
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_UTILS_CPP_FUNCTIONAL_H