OpenBLAS: blacklist unsupported clang

[catap]

Description

Closes: https://trac.macports.org/ticket/68225

Type(s)

• bugfix

Tested on

macOS x.y
Xcode x.y / Command Line Tools x.y.z

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[macportsbot]

Notifying maintainers:
@michaelld for port OpenBLAS.
@NicosPavlov for port OpenBLAS.

[cjones051073]

I am not convinced this is really the right/complete fix here, and that the issues run much deeper. See my post to https://trac.macports.org/ticket/68225

[catap]

I agree with @cjones051073 at the ticket that blacklisting won't help