1. With a Clang that doesn't default to GNU extensions they need to be enabled explicitly.
2. The X86 directory lit config sets it already, there's no reason for this test to do it by itself.
3. The C frontend executable will fail if there's for example a Clang resource file for the C++ mode that sets C++-specific options:
```
+ /home/tambre/dev/llvm/build/bin/clang --target=x86_64-unknown-linux-gnu -fPIE -fuse-ld=lld -Wl,--unresolved-symbols=ignore-all -pie -fPIC -shared /home/tambre/dev/llvm/bolt/test/R_ABS.pic.lld.cpp -o /home/tambre/dev/llvm/build/tools/bolt/test/Output/R_ABS.pic.lld.cpp.tmp.so -Wl,-q -fuse-ld=lld
clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]
error: invalid argument '-std=c23' not allowed with 'C++'
```
Replace a single dash with a double dash for options that have more
than a single letter.
llvm-bolt-wrapper.py has special treatment for output options such as
"-o" and "-w" causing issues when a single dash is used, e.g. for
"-write-dwp". The wrapper can be fixed as well, but using a double dash
has other advantages as well.
Reviewed By: rafauler
Differential Revision: https://reviews.llvm.org/D127538
