cargo config: filter -Clinker from rustflags

linker pass through rustflags will fail to be resolved from build
script. So, we have to filter this flags out from rustflags and add
a dedicated specific target entry in config.toml.

src/outpost/barbican/_internals/cargo_config.py

@@ -16,13 +16,19 @@ def run_cargo_config(rustargs: Path, target: Path, extra_args: str, outdir: Path
     target = target.read_text().splitlines()[0]
     rustargs = rustargs.read_text().splitlines()
     rustargs.extend(extra_args.split(" "))
+    linkerargs = list(filter(lambda x: x.startswith("-Clinker"), rustargs))
+    linker = linkerargs[0].split("=")[1] if len(linkerargs) else "is not set"
+    rustargs = list(filter(lambda x: not x.startswith("-Clinker"), rustargs))
 
     config = f"""
 [build]
 target = "{target}"
 target-dir = "{str(outdir.resolve())}"
 rustflags = {rustargs}
 
+[target.{target}]
+{"#" if not len(linkerargs) else ""}linker = "{linker}"
+
 [env]
 OUT_DIR = "{str(outdir.resolve())}"
 """