cmake: create MSVC-compatible physfs.pc

[madebr]

Fixes #125

• I confirm that I am the author of this code and release it to the PhysicsFS project under the zlib license. This contribution does not contain code from other sources, including code generated by a Large Language Model ("AI").

Creates the following file for a shared build:

prefix=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix
exec_prefix=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix
libdir=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix/lib
includedir=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix/include

Name: PhysicsFS
Description: PhysicsFS is a library to provide abstract access to various archives.
URL: https://icculus.org/physfs/
Version: 3.3.0
Requires.private: sdl3
Libs: -LIBPATH:${libdir} physfs.lib
Cflags: -I${includedir}

and the following for a static build:

prefix=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix
exec_prefix=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix
libdir=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix/lib
includedir=C:/home/maarten/source/repos/physfs/cmake-build-debug/prefix/include

Name: PhysicsFS
Description: PhysicsFS is a library to provide abstract access to various archives.
URL: https://icculus.org/physfs/
Version: 3.3.0
Requires.private: sdl3
Libs: -LIBPATH:${libdir} physfs-static.lib
Cflags: -I${includedir}