[clang] [Clang] Fix missed initializer instantiation bug for variable templates (PR #138122)

[Paul Kirth via cfe-commits]

ilovepi wrote:

I have a revert up for this in #140930, due to the regressions reported in #140773, which breaks Fuchsia builds with new toolchains. We're fairly certain that changing the instantiation order as done in the patch is the root cause of the regression. 

https://github.com/llvm/llvm-project/pull/138122