add run-make test for -C linker-flavor=gcc:*

ensures that the wrapped linker is indeed passed straight to cc

Author: lqd

src/test/run-make/gcc-linker-flavor/Makefile

@@ -0,0 +1,9 @@
+# only-linux
+
+# Ensure that the enriched `gcc` linker-flavor passes the requested linker to `cc`
+
+-include ../../run-make-fulldeps/tools.mk
+RUSTC_FLAGS = -C linker-flavor=gcc:my_wrapped_linker -Z unstable-options --print link-args
+
+all:
+	$(RUSTC) $(RUSTC_FLAGS) empty.rs | $(CGREP) "fuse-ld=my_wrapped_linker"

src/test/run-make/gcc-linker-flavor/empty.rs

@@ -0,0 +1,4 @@
+// Test ensuring that the enriched `gcc` linker flavor requesting an arbitrary linker (`-C
+// linker-flavor=gcc:$linker`) is passed to `cc` as `-fuse-ld`
+
+fn main() {}