feat(CMakeLists): Add MSVC-specific compiler warning flags in CMake configuration

[scc-tw]

Summary:
This pull request improves the handling of MSVC compiler warning flags in the CMake build configuration. Previously, the MSVC compiler warning flags (C_FLAGS and CXX_FLAGS) were unset, resulting in limited warning coverage. This change explicitly defines and applies a comprehensive set of MSVC warnings for improved code quality and consistency.

Key Changes:

• Removed the placeholder comments and empty flag settings for MSVC (C_FLAGS and CXX_FLAGS).
• Introduced a dedicated list MSVC_WARNING_FLAGS with a clear set of warning flags:
  • /W4: Comprehensive warnings similar to GCC's -Wall.
  • Enabled critical warnings to detect potential code issues related to declaration hiding (/we4456, /we4457, /we4458).
  • Disabled overly verbose or less useful warnings (/wd4100, /wd4324).

Rationale:

• This improves the maintainability of the build process by explicitly defining relevant MSVC warnings.
• It ensures better parity with warning standards established for GCC/Clang builds.

Testing:

• Successfully compiled and verified locally with MSVC.
• No negative impact observed on performance benchmarks (llama-perplexity and llama-bench).

Review Considerations:

• Reviewers should confirm these warnings align with the project's coding standards and practices.

[scc-tw]

Do we need to fix these CI failures? These are expected warnings that Windows MSVC tends to be noisy about, such as:

• Conversion from 'uint32_t' to 'ggml_fp16_t', possible loss of data
• Unreachable code
• Warning C5105: Macro expansion producing 'defined' has undefined behavior
• etc.

These issues do not occur with GCC or Clang when -Wall -Wextra is enabled.