Fix C_ASSERT linkage conflicts when building with MinGW-w64

[conorKotwasinski]

This PR fixes a compilation error that occurs when building Detours with MinGW-w64 toolchain. The issue arises from conflicting C_ASSERT declarations between ws2tcpip.h (C++ linkage) and detours.h (C linkage).

The fix moves C_ASSERT declarations out of the extern "C" block to preserve C++ linkage consistently. This allows Detours to compile successfully with MinGW-w64 while maintaining the same behavior.

Specifically:

• Moved size verification C_ASSERTs outside of extern "C" block
• Maintains functionality while resolving the linkage conflict
• Allows successful compilation with MinGW-w64 toolchain

This is important for projects using MinGW-w64 to build applications that depend on Detours, particularly when working with network-related functionality that requires ws2tcpip.h.

Before this change, attempting to build with MinGW-w64 would fail with:
conflicting declaration of 'void __C_ASSERT__(int*)' with 'C' linkage

The fix allows seamless integration while keeping the original verification logic intact.

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