Apply system_shared_libs to all variants

Remove the odd semantics of system_shared_libs that ignore the property
for non-bionic variants by always honoring it.  For the common case
of system_shared_libs: [] this is generally correct, a non-bionic
variant of a module that doesn't compile against bionic libc probably
also doesn't want some other libc.  For modules that use something
like system_shard_libs: ["libc"] to link against libc but not libdl
and libm this may cause problems, as it will cause a host varaint to
try to link against the non-existent host "libc" module, but there
aren't very many of those and they can be fixed to use a target.bionic
clause.

Bug: 193559105
Test: m checkbuild
Change-Id: I94454a71144e3e68c7148b8d0bf2d974d2ad2bc6
diff --git a/cc/linker.go b/cc/linker.go
index 13df232..14564b6 100644
--- a/cc/linker.go
+++ b/cc/linker.go
@@ -15,9 +15,10 @@
 package cc
 
 import (
+	"fmt"
+
 	"android/soong/android"
 	"android/soong/cc/config"
-	"fmt"
 
 	"github.com/google/blueprint"
 	"github.com/google/blueprint/proptools"
@@ -244,8 +245,7 @@
 	if linker.Properties.System_shared_libs != nil && linker.Properties.Default_shared_libs != nil {
 		ctx.PropertyErrorf("system_shared_libs", "cannot be specified if default_shared_libs is also specified")
 	}
-	if ctx.toolchain().Bionic() && linker.Properties.System_shared_libs != nil {
-		// system_shared_libs is only honored when building against bionic.
+	if linker.Properties.System_shared_libs != nil {
 		return linker.Properties.System_shared_libs
 	}
 	return linker.Properties.Default_shared_libs