`main` is not the only main function in Windows. You can choose one
from these four -- {w,}{WinMain,main}. There are four different entry
point functions for them, {w,}{WinMain,main}CRTStartup, respectively.
The linker needs to choose the right one depending on which `main`
function is defined.

llvm-svn: 238667

The new mechanism is less code, and fixes the case where all inputs
are archives.

Differential Revision: http://reviews.llvm.org/D10136

llvm-svn: 238618

This is an initial patch for a section-based COFF linker.

The patch has 2300 lines of code including comments and blank lines.
Before diving into details, you want to start from reading README
because it should give you an overview of the design.

All important things are written in the README file, so I write
summary here.

- The linker is already able to self-link on Windows.

- It's significantly faster than the existing implementation.
  The existing one takes 5 seconds to link LLD on my machine,
  while the new one only takes 1.2 seconds, even though the new
  one is not multi-threaded yet. (And a proof-of-concept multi-
  threaded version was able to link it in 0.5 seconds.)

- It uses much less memory (250MB vs. 2GB virtual memory space
  to self-host).

- IMHO the new code is much simpler and easier to read than
  the existing PE/COFF port.

http://reviews.llvm.org/D10036

llvm-svn: 238458