Add a new interceptors for cdbr(3) and cdbw(3) API from NetBSD

Summary:
cdb - formats of the constant database.

cdbr, cdbr_open, cdbr_open_mem, cdbr_entries, cdbr_get, cdbr_find,
cdbr_close - constant database access methods.

cdbw_open, cdbw_put, cdbw_put_data, cdbw_put_key, cdbw_stable_seeder,
cdbw_output, cdbw_close - creates constant databases.

Add a dedicated test for this API.

Reviewers: vitalybuka, joerg

Reviewed By: vitalybuka

Subscribers: kubamracek, llvm-commits, mgorny, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D55167

llvm-svn: 349021