build: set ZSTD_LEGACY_SUPPORT=0 in remaining build systems

build: set ZSTD_LEGACY_SUPPORT=0 in remaining build systems

Summary:
Completes the transition to disabled legacy support by default across all build systems. This follows up on the previous Makefile and CMake changes to ensure consistent default behavior regardless of the build system used.

Updated build configurations: Meson, tests/Makefile, Visual Studio 2008/2010 projects, and BUCK.

Test Plan:
Verified changes compile correctly via `make lib-release`. Build system configurations have been updated consistently across all platforms.