rust: Use host linker when building for Mac host.

This behavior is non-hermetic, but matches the behavior of the C++
support. On Linux, using lld works, but on OSX, this fails because lld
does not support Apple's new .tbd files.

Bug: 155302034
Test: On both Linux and Mac hosts:
    cd external/rust; mma

Change-Id: I0ad489113d720bdb9c3b7a67cce9d1e72266f428
diff --git a/rust/config/global.go b/rust/config/global.go
index e1b1775..2020f46 100644
--- a/rust/config/global.go
+++ b/rust/config/global.go
@@ -54,6 +54,9 @@
 		"-Wl,--pack-dyn-relocs=android+relr",
 		"-Wl,--no-undefined",
 		"-Wl,--hash-style=gnu",
+
+		"-B${ccConfig.ClangBin}",
+		"-fuse-ld=lld",
 	}
 )
 
@@ -80,7 +83,7 @@
 
 	pctx.ImportAs("ccConfig", "android/soong/cc/config")
 	pctx.StaticVariable("RustLinker", "${ccConfig.ClangBin}/clang++")
-	pctx.StaticVariable("RustLinkerArgs", "-B ${ccConfig.ClangBin} -fuse-ld=lld")
+	pctx.StaticVariable("RustLinkerArgs", "")
 
 	pctx.StaticVariable("DeviceGlobalLinkFlags", strings.Join(deviceGlobalLinkFlags, " "))