base_macros.h disables warnings without push/pop, leaking them into consumer translation units

Description

strings/base_macros.h disables four MSVC warnings with bare #pragma warning(disable: ...) and no matching push / pop:

#ifdef _MSC_VER
// Note: this is a workaround for a false-positive warning produced by the Visual C++ 15.9 compiler.
#pragma warning(disable : 5046)

// Note: this is a workaround for a false-positive warning produced by the Visual C++ 16.3 compiler.
#pragma warning(disable : 4268)

// C++ module warnings by /W4
#pragma warning(disable : 4499)
#pragma warning(disable : 4630)
#endif // _MSC_VER

base.h includes base_macros.h near the top and never restores the warning state. C5046, C4268, C4499 and C4630 therefore stay disabled for the remainder of every translation unit that includes <winrt/base.h>, which includes all of the consumer's own code that follows the include.

The first two disables are documented as workarounds for Visual C++ 15.9 and 16.3, while the latter two were added for early C++ module support. Current supported toolsets no longer emit these warnings for C++/WinRT, so retaining the pragmas only suppresses diagnostics in consumer code.

Repro

// leak.cpp
namespace { struct S { int x; }; }
S f();
int main() { f(); return 0; }

cl /c /std:c++20 /permissive- /W4 leak.cpp
leak.cpp(3): warning C5046: 'f': Symbol involving type with internal linkage not defined

Add the include and the warning disappears, even though the offending code is unchanged and is entirely outside C++/WinRT:

#include <winrt/base.h>
namespace { struct S { int x; }; }
S f();
int main() { f(); return 0; }

cl /c /std:c++20 /permissive- /W4 /I<sdk> leak.cpp
(no diagnostics)

Reproduced with both /W4 and /Wall on MSVC x64.

This is the only unscoped suppression in the tree

Auditing every warning pragma under strings/:

Every other suppression in the project is already correctly scoped, so this looks like an oversight rather than a deliberate choice.

Fix

Remove all four obsolete disables from base_macros.h. This fixes every inclusion path uniformly and avoids adding warning-state plumbing for diagnostics that current compilers no longer produce.

The official MSVC off-by-default warning list does not include any of the four warning numbers. A rich generated-header translation unit compiles under /Wall with both v143 and v145 without any of them, and the v145 named-module target also rebuilds under /Wall without any of them. The original consumer repro reports C5046 again.

Fixed in #1625.

Relationship to #1623

#1623 adds a file-level diagnostic scope to every generated header, which would incidentally contain these disables inside base.h as a side effect. I am raising and fixing this separately because it is a distinct bug with its own repro, and because it should be fixed whether or not #1623 is taken.

Inspect strings/base_macros.h and the MSVC warning pragmas described in the issue. Reproduce the leak with the provided leak.cpp example under /W4 or /Wall, then verify that the warnings return after the change and that the relevant C++/WinRT headers still build cleanly; the issue notes this was fixed in #1625.