[PECOFF] Do not wrap the linker internal file with an archive file.

We wrapped the linker internal file with a virtual archive file, so that the
linker internal file was linked only when it's actually used. This was to avoid
__ImageBase being included to the resulting executable. __ImageBase used to
occupy four bytes when emitted to executable.

And then it turned out that the implementation of __ImageBase was wrong -- it
shouldn't have been a regular atom but an absolute atom. Absolute atoms point
to some memory location, but they don't occupy disk space themselves. So it
wouldn't increase executable size (except the symbol table.) That means that
it's OK to link the linker internal file unconditionally.

So this patch does that, removing the wrapper archive file. Doing this
simplifies the code.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194127 91177308-0d34-0410-b5e6-96231b3b80d8
Undef a local macro after use.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@194128 91177308-0d34-0410-b5e6-96231b3b80d8