Shaves ~45KB off of binary size in an ANGLE build on Linux, coming from
the built-in TVariable and TFunction variables.

Bug: angleproject:4889
Change-Id: I5466c9e26b069a07bf52d00fc2a9c5d49f3c0feb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2958868Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>