The _LIBCPP_PSTL_CUSTOMIZATION_POINT macro was assuming that the policy
was called _RawPolicy and referencing it by name. It happened to always
work but this was definitely accidental and an oversight in the original
implementation. This patch fixes that by passing the policy to the macro
explicitly. Noticed while reviewing #66968.
Those were found while trying to enable configurations like no-threads
and no-localization with Clang modules enabled.
Differential Revision: https://reviews.llvm.org/D153977