Remove clang-sys dependency

[CGMossa]

This PR accomplishes three very distinct things:

• Adds a missing : infront of cargo:: everywhere.
• Adds metadata, which have been missing from build.rs forever
  Update: the above items are unnecessary. rust 1.77 have a new syntax for build.rs. I didn't
  catch that initially. This has now been reverted, and MSRV for this PR is the same.
• Removes the inclusion of clang/clang-sys, by instead of the elaborate processing, we instead, ignore all items coming from headers that aren't the R-headers.

[yutannihilation]

I didn't know the new syntax. Is it your intention to drop
the support on Rust <1.77?

Stick to cargo: only if the support of Rust version older than 1.77 is required.

https://doc.rust-lang.org/cargo/reference/build-scripts.html

[CGMossa]

Wow! Thanks! I did not know about syntax change in cargo 1.77. Yesterday, while I was trying to make this strategy work, I tried everything, and then I thought we had used the wrong syntax.

I've reverted this.

@Ilia-Kosenkov You asked about the Rcomplex thing. Since we are filtering elements in a new way, maybe now,
there is an element not being filtered, or something like that. But I just checked, and our definition of Rcomplex is still the same.
The items from wrapper.h are being considered just fine.

[CGMossa]

So one explanation to the extra new items that somewhat looks like:

enum {SORTED_DECR_NA_1ST = -2,
      SORTED_DECR = -1,
      UNKNOWN_SORTEDNESS = INT_MIN, /*INT_MIN is NA_INTEGER! */
      SORTED_INCR = 1,
      SORTED_INCR_NA_1ST = 2,
      KNOWN_UNSORTED = 0};

these are items that stem from an anonymous C-enum. Before, with the clang-processing, we would just ignore it.
This time, it is being included. There is zero harm with it being present.