The libEGL_angle.so and libGLESv2_angle.so libraries are typically
loaded into the same process each time, so we need to make sure there
aren't any duplicated symbols which could violate ODR and lead to
crashes or undefined behavior.   In this case, the libEGL_angle.so
function pointer names were colliding with libGLESv2_angle.so function
names, causing crashes at runtime.   The fix here is to mark the
libEGL_angle.so function pointer symbols 'hidden', so they don't appear
in the symbol table for other executables/libraries to see and can't be
overridden by other symbols.

Bug: angleproject:3751
Test: Embed ANGLE within dEQP.apk and verify no crashes
Change-Id: Ibb78369374a4a68b3489a7dd7775c52e29fa37e0
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1724909
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>