Add Toolchain.Bionic()

Move some cc ctx.Host() / ctx.Device() checks over to using
ctx.toolchain().Bionic(). There will be more changes, these are just the
obvious ones dealing with host_ldlibs / crt / system libraries.

Bug: 31559095
Test: out/soong/build.ninja is identical
Change-Id: Ibba60483b4ab0e01f6996eb7d883120e4acc1830
diff --git a/cc/config/x86_darwin_host.go b/cc/config/x86_darwin_host.go
index 2db3cbf..a6d4aaf 100644
--- a/cc/config/x86_darwin_host.go
+++ b/cc/config/x86_darwin_host.go
@@ -269,6 +269,10 @@
 	return darwinAvailableLibraries
 }
 
+func (t *toolchainDarwin) Bionic() bool {
+	return false
+}
+
 var toolchainDarwinX86Singleton Toolchain = &toolchainDarwinX86{}
 var toolchainDarwinX8664Singleton Toolchain = &toolchainDarwinX8664{}