protobuf: do not use symlinks

[meator]

Symlinks on Windows can be problematic. This PR replaces them with simple copies.

To make this change, it would be useful to know what even is the purpose of the symlink:

wrapdb/subprojects/packagefiles/protobuf/src/meson.build

Lines 2 to 11 in 92719d5

	python = find_program('python3')
	proto_includes_link = custom_target(
	'proto_includes_link',
	input: files('symlink.py'),
	output: 'include', # directory adjacent to protoc binary
	command: [python, '@INPUT@', meson.current_source_dir(), '@OUTPUT@'],
	)
	proto_includes_link_dep = declare_dependency(
	sources: proto_includes_link,
	)

The wrap builds without it (and with all proto_includes_link_dep dependencies removed). If there is some elegant way to remove this entirely, it should be preferred.

What is the purpose of the symlink?

[meator]

CI failure is not caused by this PR.

[bgilbert]

It was added in #1263 to address #1259.

[bgilbert]

Why not copy on Windows and symlink otherwise?