setup-toolchain.sh: When translating -arch to -target, keep the origi…

…nal -arch as well

The clang driver does a number of rewrites back and forth between
arch names and triples. For aarch64/arm64, an input -arch arm64 or
-target arm64-apple-darwin ends up rewritten to aarch64-apple-darwin,
but at different stages (and -target aarch64-apple-darwin doesn't work
at all with current clang versions).

Keep the -arch argument, so that we follow the same path of arch/triple
rewrites as the original clang, so that -dumpmachine prints the same
value for -arch arm64 as it does on macos without this wrapper script
(printing aarch64-apple-darwin*).

setup-toolchain.sh

@@ -55,7 +55,7 @@ while [ \$# -gt 0 ]; do
 	a=\$1
 	if [ "\$a" = "-arch" ]; then
 		shift
-		ARGS+=(-target \$1-apple-darwin16)
+		ARGS+=(-target \$1-apple-darwin16 -arch \$1)
 		TARGET_SET=1
 		shift
 	else