[clang] [flang] [clang][driver] When -fveclib=ArmPL flag is in use, always link against libamath (PR #116432)

[Paul Osmialowski via cfe-commits]

pawosm-arm wrote:

As I prepared a piece of code which makes the `-l` flags being treated properly when read from a config file (so it won't result in unresolved symbols e.g. when used with `-static`), I realized that going the config file way still creates a problem: with `-fveclib=ArmPL -lamath` put into a config file, it will always be linked with `libamath`, even if the user decides to use `-fveclib=none` to override this. And situation of this kind can only be solved properly by the patch discussed in this PR.

And there's another rationale behind it I can think of: using `-fopenmp` does not require the user to add `-lomp` to the command line, it just happens automatically. The sheer logic demands that `-fveclib=ArmPL` should result in the same treatment. There is no other provider for ArmPL's veclib functions these days than libamath.


https://github.com/llvm/llvm-project/pull/116432