libsodium-sys requires memset_explicit which is not available in older
MinGW toolchains. Added a C shim that provides a fallback implementation
using volatile pointers to prevent compiler optimization.
Changes:
- Added memset_s_shim.c with fallback memset_explicit implementation
- Updated build.rs to compile shim for Windows GNU targets
- Added cc crate as build dependency
- Set CFLAGS in CI to target Windows 8+ (_WIN32_WINNT=0x0602)
- Set SODIUM_STATIC=yes to force static libsodium build
Fixes linking error: undefined reference to memset_explicit
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
