Make it possible to load libGLESv2 and OpenCL_ANGLE without adding
ANGLE's binary directory to the search path.

Bug: angleproject:5904
Change-Id: Ie810466b39e1101e4da5b9fd199d26683b129281
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2897250
Commit-Queue: John Plate <jplate@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>