Add initial support for creating shared library with symbol versioning

[parth-07]

This commit adds initial support for building shared libraries with
symbol versioning information. Symbol versioning allows to add version
information to symbols. It is used to provide multiple definitions of
the same symbol for backward compatibility.

This commit adds the support such that the functionality can be enabled
conditionally at build time by specifying ELD_ENABLE_SYMBOL_VERSIONING
CMake option. This commit also updates the PR checkin builder to enable
symbol versioning functionality.

Symbol versioning is a target-independent feature but requires support
from compiler, linker and the loader. From the ELF perspective, symbol
versioning is implemented using 3 sections:
.gnu.version(SHT_GNU_versym), .gnu.version_d(SHT_GNU_verdef), and
.gnu.version_r(SHT_GNU_verneed). This commit only provides support for
.gnu.version and .gnu.version_d sections because only they are required
when building a shared library. .gnu.version_r is required when using a
shared library. Briefly, these sections can be descrbed as:

• .gnu.version: An array of version IDs. i'th entry of this array stores
  the version ID of the i'th symbol in the dynamic symbol
  table.
• .gnu.version_d: Stores the version definitions of the symbols that
  are defined by this module.
• .gnu.version_r: Stores the version definitions of the undefined symbols that
  are used by this module.

To add the support for creating shared libraries with symbol versioning
information, this commit:

• Adds support for creating symbol versioning sections .gnu.version and
  .gnu.version_d
• Improve version script support to properly handle versioned
  nodes.
• Add logic to properly assign output version IDs to symbols.
• Update dynamic symbol table and .hash section to properly emit
  versioned symbols.
• Emit symbol versioning sections and correctly fill symbol versioning
  information in the .dynamic section.

Additionally, this commit adds the trace flag --trace=symbol-versioning.

Resolves #646

[quic-seaswara]

We need to define the symbol override rules especially for weak and strong symbols that have versioning information.

Does this work with --gc-sections ?

Can you please add the tests applicable ?

Please use lld to build with versioned libraries generated by eld, and run it to make sure we have those cases handled.

[parth-07]

We need to define the symbol override rules especially for weak and strong symbols that have versioning information.

This PR does not add support for the case where the input files have versioned symbols. This PR only enables creating shared libraries with symbol versioning information. So, there is no symbol resolution change for this PR.

Does this work with --gc-sections ?

Yes, --gc-sections should work as before. This PR does not modify the garbage-collection stage. Garbage-collection and version scripts behave as before.

Please use lld to build with versioned libraries generated by eld, and run it to make sure we have those cases handled.

I have added build and run tests for symbol versioning in x86-64.

[parth-07]

Thank you @quic-seaswara, @quic-areg and @quic-akaryaki for the reviews. I have resolved / replied-to all the reviews. Can you please review again?

[quic-areg]

LGTM