Partial revert of "Use std::foo_t rather than std::foo in LLVM." in googlebench

[jroelofs]

Summary

Since googlebench builds as c++11, the change there is incorrect and breaks the
googlebench build when the STL implementation is strict about std::enable_if_t
not being available in lesser c++ versions.

partial revert of: 1bd6123b781120c9190b9ba58b900cdcb718cdd1 (https://reviews.llvm.org/D74384)

[MaskRay]

How about just using C++14 for utils/benchmark/ ?

[jroelofs]

In D101583#2727459, @MaskRay wrote:

How about just using C++14 for utils/benchmark/ ?

That seemed like a bigger change, with more potential fallout re: windows bots that I didn't want to sign up for ;)

[MaskRay]

In D101583#2727485, @jroelofs wrote:

In D101583#2727459, @MaskRay wrote:

How about just using C++14 for utils/benchmark/ ?

That seemed like a bigger change, with more potential fallout re: windows bots that I didn't want to sign up for ;)

llvm/CMakeLists.txt sets CMAKE_CXX_STANDARD to 14.

[jroelofs]

In D101583#2727555, @MaskRay wrote:

llvm/CMakeLists.txt sets CMAKE_CXX_STANDARD to 14.

As "prior art", https://reviews.llvm.org/D93794 also backed out a c++14 feature from this component.

Seems prudent to keep our diff with upstream googlebench as small as possible to make it easier to update in the future.

[MaskRay]

In D101583#2727593, @jroelofs wrote:

In D101583#2727555, @MaskRay wrote:

llvm/CMakeLists.txt sets CMAKE_CXX_STANDARD to 14.

As "prior art", https://reviews.llvm.org/D93794 also backed out a c++14 feature from this component.

Seems prudent to keep our diff with upstream googlebench as small as possible to make it easier to update in the future.

OK, did not know this is a local difference. If that is the case, LG.

llvm/utils/benchmark/src/sysinfo.cc

 bool GetSysctl(std::string const& Name, std::string* Out) {
   Out->clear();
   auto Buff = GetSysctlImp(Name);
   if (!Buff) return false;
   Out->assign(Buff.data());
   return true;
 }
 
-template <class Tp, class = std::enable_if_t<std::is_integral<Tp>::value>>
-bool GetSysctl(std::string const &Name, Tp *Out) {
+template <class Tp,
+          class = typename std::enable_if<std::is_integral<Tp>::value>::type>
+bool GetSysctl(std::string const& Name, Tp* Out) {
   *Out = 0;
   auto Buff = GetSysctlImp(Name);
   if (!Buff) return false;
   *Out = static_cast<Tp>(Buff.GetAsUnsigned());
   return true;
 }
 
 template <class Tp, size_t N>