Create symlink for bionic files

This change creates following symlinks for bionic files.

/system/lib/libc.so -> /apex/com.android.runtime/lib/bionic/libc.so
/system/lib/libm.so -> /apex/com.android.runtime/lib/bionic/libm.so
/system/lib/libdl.so -> /apex/com.android.runtime/lib/bionic/libdl.so
/system/bin/linker -> /apex/com.android.runtime/bin/linker
...

This allows us to not have mountpoints under /bionic.

Bug: 125549215
Test: m and inspect the symlinks in the system partition.
Change-Id: I3a58bf4f88c967862dbf06065a1af8fc4700dda3

cc/util.go

@@ -133,3 +133,10 @@ func splitFileExt(name string) (string, string, string) {
 
 	return root, suffix, ext
 }
+
+// linkDirOnDevice/linkName -> target
+func makeSymlinkCmd(linkDirOnDevice string, linkName string, target string) string {
+	dir := filepath.Join("$(PRODUCT_OUT)", linkDirOnDevice)
+	return "mkdir -p " + dir + " && " +
+		"ln -sf " + target + " " + filepath.Join(dir, linkName)
+}