The os_log helper functions are linkonce_odr and supposed to be
uniqued across TUs, so attachine a DW_AT_decl_line on it is highly
misleading. By setting the function decl to implicit, CGDebugInfo
properly marks the functions as artificial and uses a default file /
line 0 location for the function.
rdar://problem/63450824
Differential Revision: https://reviews.llvm.org/D80463
Adrian Prantl