Move system_shared_libs into target.bionic clause

Use target.bionic.system_shared_libs when it is used to limit the
default shared libraries (as opposed to remove them completely).
This avoids attempting to add a host dependency on libc when
system_shared_libs is modified to apply to all variants.

Bug: 193559105
Test: m checkbuild
Change-Id: I6cf8e90424431b5abb8ddb32dbf7dfd7a4b8570a
diff --git a/Android.bp b/Android.bp
index f94feb0..742996b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -102,8 +102,10 @@
     recovery_available: true,
     srcs: libpcre2_src_files,
     stl: "none",
-    system_shared_libs: ["libc"],
     target: {
+        bionic: {
+            system_shared_libs: ["libc"],
+        },
         linux_bionic: {
             enabled: true,
         },