Bug in the test suite of LLVM 18.X with rpath wrapping

[Crivella]

Problem observed during the builds:

• {compiler}[GCCcore/13.3.0] LLVM 18.1.8 (new) #21832 (comment)
• {compiler}[SYSTEM] LLVM 18.1.8 (new)  #21833 (comment)

The error seems to happens due to the rpath wrappers being as the compilers during the test step, which, when executed with -Werror makes the detection of the allowed --std=... flags fails due to errors of the type -Wunused-command-line-argument.

[Crivella]

Fixed with the introduction of LLVM-19.1.7_clang_rpathwrap_test.patch together with the EC files