[clang] [clang][Modules] Raise empty.modulemap expected size to <70KB to fix RISC-V failure (PR #123959)

[Alex Bradbury via cfe-commits]

asb wrote:

Thanks, I've gone ahead an merged. Any insight into why the module files may be larger on RISC-V vs other targets greatly appreciated - as I said in https://github.com/llvm/llvm-project/pull/111360 I'm not sure how to best inspect the module files.

https://github.com/llvm/llvm-project/pull/123959