formula: set CMAKE_PROGRAM_PATH to use shims

[cho-m]

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We probably need to keep CMAKE_PREFIX_PATH environment variable as it is cleanest way of handling nested and indirect cmake usage.

See https://cmake.org/cmake/help/latest/command/find_program.html for details on search order,

• CMAKE_PROGRAM_PATH cache variable is 2nd
• CMAKE_PREFIX_PATH environment variable is 3rd
• PATH is 5th

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An alternative could be using more specific alternatives to CMAKE_PREFIX_PATH. There are a number of things the variable impacts, e.g.

• find_package - probably main use we want. We could consider scanning deps for CMake files and using <PackageName>_DIR environment variables instead though may need to be careful to avoid overriding CLT and make sure case-sensitive name.
• find_program - I would guess we mainly want to find these via PATH
• find_library - we set CMAKE_LIBRARY_PATH/CMAKE_FRAMEWORK_PATH already so may cover many cases
• find_file - ? CMAKE_INCLUDE_PATH could cover some of this
• find_path - ? CMAKE_INCLUDE_PATH could cover some of this

[carlocab]

Suggested change

	def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework: "LAST",
	program_path: ENV["PATH"]&.split(File::PATH_SEPARATOR))
	def std_cmake_args(install_prefix: prefix, install_libdir: "lib", find_framework: "LAST")

I suggest just using the contents of ENV["PATH"] unconditionally unless we know there are formulae that need to set this.

[MikeMcQuaid]

Makes sense. Have been thinking we probably want some more CMake handling like this