[clang-tidy] Disable google-runtime-int in Objective-C++ 🔓

Summary:
In contrast to Google C++, Objective-C often uses built-in integer types
other than `int`. In fact, the Objective-C runtime itself defines the
types NSInteger¹ and NSUInteger² which are variant types depending on
the target architecture. The Objective-C style guide indicates that
usage of system types with variant sizes is appropriate when handling
values provided by system interfaces³. Objective-C++ is commonly the
result of conversion from Objective-C to Objective-C++ for the purpose
of integrating C++ functionality. The opposite of Objective-C++ being
used to expose Objective-C functionality to C++ is less common,
potentially because Objective-C has a signficantly more uneven presence
on different platforms compared to C++. This generally predisposes
Objective-C++ to commonly being more Objective-C than C++. Forcing
Objective-C++ developers to perform conversions between variant system types
and fixed size integer types depending on target architecture when
Objective-C++ commonly uses variant system types from Objective-C is
likely to lead to more bugs and overhead than benefit. For that reason,
this change proposes to disable google-runtime-int in Objective-C++.

[1] https://developer.apple.com/documentation/objectivec/nsinteger?language=objc
[2] https://developer.apple.com/documentation/objectivec/nsuinteger?language=objc
[3] "Types long, NSInteger, NSUInteger, and CGFloat vary in size between
32- and 64-bit builds. Use of these types is appropriate when handling
values exposed by system interfaces, but they should be avoided for most
other computations."
https://github.com/google/styleguide/blob/gh-pages/objcguide.md#types-with-inconsistent-sizes

Subscribers: xazax.hun, jdoerfert, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59336

llvm-svn: 356627