`std::abs(x - y)` where x and y are unsigned integers fails to compile
with an "call of overloaded 'abs(unsigned int)' is ambiguous" error
on GCC, and even if it did compile, that expression still wouldn't
give the correct result since `x - y` is unsigned.
Without included header build fails on gcc-10 as:
```
[ 13%] Building CXX object Source/Core/AudioCommon/CMakeFiles/audiocommon.dir/CubebUtils.cpp.o
In file included from ../../../../Source/Core/AudioCommon/CubebUtils.cpp:13:
../../../../Source/Core/Common/StringUtil.h: In function 'bool TryParse(const string&, T*)':
../../../../Source/Core/Common/StringUtil.h:84:20: error: 'numeric_limits' is not a member of 'std'
84 | if (value < std::numeric_limits<LimitsType>::min() ||
| ^~~~~~~~~~~~~~
```
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
So far in all our uses of ScopeGuard, the type of the callable is
usually just a lambda or a function pointer, so there is no need
to rely on std::function's type erasure.
While the cost of using std::function is probably negligible, it still
causes some unnecessary overhead that can be avoided by making
ScopeGuard a templated class. Thanks to class template argument
deduction in C++17 most existing usages do not even need to be changed.
See https://godbolt.org/z/KcoPni for a comparison between
a ScopeGuard that uses std::function and one that doesn't