Make -lpthread -lm -lrt -ldl --as-needed on Linux target

[dlangBugzillaToGithub]

Vic Luo reported this on 2018-07-22T09:38:18Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=19106

CC List

• Vic Luo

Description

Current implementation links these libraries under all circumstances. However, for libc-free programming these libraries are redundant. This is one of the show stoppers toward `dmd`-based libc-free programming without invoking `cc` manually. Another is https://github.com/dlang/dmd/pull/794.

Related code: https://github.com/dlang/dmd/blob/6371942b1bf26dc6c65cc7e0668bc82e1974c18d/src/dmd/link.d#L652