Drop /root when installing symbols

This change fixes a problem that if a module is installed to the root
partition, its symbol file appears at under symbols/root, which is an
non-existing path at runtime. Since the symbol paths should match with
the runtime path, drop /root when installing symbols.

Bug: 123985838
Test: m libc.mountpoint
libc.so is found under symbols/bionic/lib[64]

Change-Id: I38bd226c3ec758d69902f4f288c83f68170c4068
diff --git a/core/soong_cc_prebuilt.mk b/core/soong_cc_prebuilt.mk
index 39cc0f0..dd33852 100644
--- a/core/soong_cc_prebuilt.mk
+++ b/core/soong_cc_prebuilt.mk
@@ -123,6 +123,8 @@
   ifdef LOCAL_SOONG_UNSTRIPPED_BINARY
     # Store a copy with symbols for symbolic debugging
     my_unstripped_path := $(TARGET_OUT_UNSTRIPPED)/$(patsubst $(PRODUCT_OUT)/%,%,$(my_module_path))
+    # drop /root as /root is mounted as /
+    my_unstripped_path := $(patsubst $(TARGET_OUT_UNSTRIPPED)/root/%,$(TARGET_OUT_UNSTRIPPED)/%, $(my_unstripped_path))
     symbolic_output := $(my_unstripped_path)/$(my_installed_module_stem)
     $(eval $(call copy-one-file,$(LOCAL_SOONG_UNSTRIPPED_BINARY),$(symbolic_output)))
     $(call add-dependency,$(LOCAL_BUILT_MODULE),$(symbolic_output))