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/library.go b/cc/library.go
index dff38c8..35d0089 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -330,7 +330,7 @@
 		deps.StaticLibs = append(deps.StaticLibs, library.Properties.Static.Static_libs...)
 		deps.SharedLibs = append(deps.SharedLibs, library.Properties.Static.Shared_libs...)
 	} else {
-		if ctx.Device() && !Bool(library.baseLinker.Properties.Nocrt) {
+		if ctx.toolchain().Bionic() && !Bool(library.baseLinker.Properties.Nocrt) {
 			if !ctx.sdk() {
 				deps.CrtBegin = "crtbegin_so"
 				deps.CrtEnd = "crtend_so"