[ELF] Fix uninitialized variables

Properly initialize _exportDynamic in ELFLinkingContext and an ELF_Sym object
created in CRuntimeFile with default values.


git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@219380 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Emit the delay-import table

This is a partial patch to emit the delay-import table. With this,
LLD is now able to emit the table that llvm-readobj can read and
dump.

The table lacks a few fields, such as the address of HMODULE, the
import address table, etc. They'll be added in subsequent patches.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@219384 91177308-0d34-0410-b5e6-96231b3b80d8