[ELF] Add more sections to the default section map.

This change adds functionality to add more sections like .gcc_except_table,
.data.rel.local, .data.rel.ro into the default section map, so that they are
all merged into appropriate output sections.

This also makes c++ static binaries comparable to what you get with the default
linker.

Adds a test for testing the functionality.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@184071 91177308-0d34-0410-b5e6-96231b3b80d8