Symbols files under $(OUT)/symbols/bionic/

We need symbol files for /bionic/* paths.

New property "mountsource" is added to specify the "real" module that
the bionic mountpoint module is a mountpoint for. The real module
provides path to the unstripped elf file, which is installed to the
symbols/bionic/* path.

Bug: 123985838
Test: m libc.mountpoint libm.mountpoint libdl.mountpoint
linker.mountpoint
$(OUT)/symbols/bionic/bin/linker, bionic/lib[64]/lib{c|dl|m}.so exist

Change-Id: I43f074f0076b576f214fe92a98689a413efd3daa
diff --git a/Android.bp b/Android.bp
index 376c250..72ab6c0 100644
--- a/Android.bp
+++ b/Android.bp
@@ -20,6 +20,7 @@
     src: "dummy_mountpoint",
     library: true,
     symlinks: ["libc.so"],
+    mountsource: "libc",
 }
 
 bionic_mountpoint {
@@ -28,6 +29,7 @@
     src: "dummy_mountpoint",
     library: true,
     symlinks: ["libdl.so"],
+    mountsource: "libdl",
 }
 
 bionic_mountpoint {
@@ -36,6 +38,7 @@
     src: "dummy_mountpoint",
     library: true,
     symlinks: ["libm.so"],
+    mountsource: "libm",
 }
 
 bionic_mountpoint {
@@ -49,4 +52,5 @@
     src: "dummy_mountpoint",
     binary: true,
     symlinks: ["linker", "linker_asan"],
+    mountsource: "linker",
 }