Add MSVC precompiled header support

[Copilot]

Extends PCH support to Microsoft Visual C++. MSVC requires compiling a .cpp stub file to create PCH, unlike GCC/Clang which compile headers directly.

Compiler Configuration (src/build-data/cc/msvc.txt)

• Added /Yc (create PCH), /Yu (use PCH), and pch suffix

Configure Script (configure.py)

• Generates stub .cpp files for MSVC: pch_lib.cpp and pch_exe.cpp containing #include "pch_lib.h"
• Sets compiler-specific variables:
  • MSVC: /Ycpch_lib.h /Fp<path> for creation, /Yupch_lib.h /Fp<path> /FIpch_lib.h for usage
  • GCC/Clang: existing -x c++-header and -include flags

Build Templates (makefile.in, ninja.in)

• Replaced hardcoded paths with pch_src_for_{lib,exe} and pch_compile_for_{lib,exe} variables
• Enables compiler-agnostic PCH rules

Example MSVC commands:

# Create PCH
cl /Ycpch_lib.h /Fpbuild/obj/pch/pch_lib.h.pch /c build/obj/pch/pch_lib.cpp

# Use PCH
cl /Yupch_lib.h /Fpbuild/obj/pch/pch_lib.h.pch /FIpch_lib.h /c src/lib/file.cpp

Maintains backward compatibility with GCC/Clang PCH support.

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