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

[David Truby via cfe-commits]

DavidTruby wrote:

> 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

I think there might be a related issue with the approach in this patch too though, in that `-fveclib=ArmPL` will silently force linking to `amath` for _all_ math functions, rather than just the veclib functions, if we add `-lamath` as in this patch. I guess this could be resolved by changing the order of the `-l` options (i.e. have `-lm` first, so that symbols from it are selected first)?

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