Revert "!UPSTREAM: Debug optimization passes."

This reverts commit fe469003eb7bc520f76b0126b4806d411ca816bb.
!UPSTREAM: attempt to fix cross-version vs/gs linking

TODO:
- Fix cloning of how_declared.
- Get rid of redundant sets of how_declared in builtin_variables.cpp.
squash! glsl: Prohibit illegal mixing of redeclarations inside/outside gl_PerVertex.

v2: Don't set "how_declared" redundantly in builtin_variables.cpp.
Properly clone "how_declared".