[clang] [clang][Modules] Reject export declarations in implementation partitions (PR #188698)

[Chuanqi Xu via cfe-commits]

================
@@ -9931,9 +9914,10 @@ class Sema final : public SemaBase {
 
   /// Is the module scope we are an implementation unit?
   bool currentModuleIsImplementation() const {
----------------
ChuanqiXu9 wrote:

OK, in this case, let's keep the name. it is kinda confusing but it is not hurting right now at least. We can add `currentModuleImplementationUnit` or something else later if needed.

https://github.com/llvm/llvm-project/pull/188698