[Bug #21779] Uniquify `InitVM` functions as well as `Init`

	Avoid possible name conflict when `--with-static-linked-ext`.

	[Bug #21779] Do not export InitVM functions

	Fix ruby/io-console#105.

	[Bug #21546] Make the generated pc file relocatable

	digest.so needs ruby/digest.h which is installed by build-ext

	Copy to path with the base name

This reverts commit 5bb946228550c7f171c27725860b153a675404f3.

Fixes https://bugs.ruby-lang.org/issues/20072

This reverts commit 1d5598fe0d3470e7cab06a756d40a9221fcd501b.

During the build, Ruby has special logic to serialize its own builtin
module to disk using the binary iseq format during the build (I assume
for speed so it doesn't have to parse builtin every time it starts
up).

However, since iseq format is architecture-specific, when building on
x86_64 for universal x86_64 + arm64, the serialized builtin module is
written with the x86_64 architecture of the build machine, which fails
this check whenever ruby imports the builtin module on arm64:

https://github.com/ruby/ruby/blob/1fdaa0666086529b3aae2d509a2e71c4247c3a12/compile.c#L13243

Thankfully, there's logic to disable this feature for cross-compiled builds:

https://github.com/ruby/ruby/blob/1fdaa0666086529b3aae2d509a2e71c4247c3a12/builtin.c#L6

This disables the iseq logic for universal builds as well.

Fixes [Bug #18286]

Not to affect other tools invoked as child processes.

On some platforms, such as FreeBSD and Oracle Linux, symbols defined
in the crt0 setup routine are exported from shared libraries.  So
ignore the symbols that would be exported even in an empty shared
library.

It does not need to be an absolute path.