[clang] Fix a crash when passing a C structure of incompatible type to a...

[clang] Fix a crash when passing a C structure of incompatible type to a function with a reference parameter.

__builtin_va_*() and __builtin_ms_va_*() are declared as functions with a
parameter of reference type.

This patch fixes a crash when using these functions in C where an argument
of structure type is incompatible with the parameter type.

Differential Revision: https://reviews.llvm.org/D82805

Reviewed By: riccibruno

Patch by: Aleksandr Platonov <platonov.aleksandr@huawei.com>