linker: the global group is added to all built-in namespaces

linker: the global group is added to all built-in namespaces

With ld.config.txt, we now have multiple built-in namespaces other than
the default namespace. Libs (and their dependents) listed in LD_PRELOAD
must be visible to those additional namespaces as well.

This also adds a debugging only feature: path to the linker config file
can be customized via LD_CONFIG_FILE environment variable. This works
only for debuggable builds.

Bug: 38114603
Bug: 62815515
Test: 1. ./external/compiler-rt/lib/asan/scripts/asan_device_setup --lib
prebuilts/clang/host/linux-x86/clang-stable/lib64/clang/5.0/lib/linux
2. enable talkback shortcut
3. in the home screen, hold vol-up/down together
4. device does not reboots and talkback shortcut is toggled
Test: bionic-unit-tests and linker-unit-tests successful

Merged-In: I9a03591053f4a9caea82f0dcb23e7a3d324bb9bd
Change-Id: I9a03591053f4a9caea82f0dcb23e7a3d324bb9bd
(cherry picked from commit 02586a2a34e6acfccf359b94db840f422b6c0231)