[cpp] - Introducing new option for c++ template to install gcc from source.

[Kaniska244]

Ref# devcontainers/images#1280

Description: New option to be introduced reinstallGccVersionFromSource to reinstall the gcc version from source overriding the default version provided by the OS.

Changelog: Following changes done for this PR.

• /src/cpp/.devcontainer/Dockerfile - Changed to introduce new option reinstallGccVersionFromSource.
• /src/cpp/.devcontainer/reinstall-gcc.sh - Added new script to reinstall gcc from source.
• /src/cpp/README.md - Updated the README with the new option details.
• /src/cpp/devcontainer-template.json - Updated the devcontainer template to define the new option.
• /test/cpp/test-utils.sh - Added test utilities for the tests to execute.
• /test/cpp/test.sh - Added test cases to validate the new option.

Checklist:

• Checked that applied changes work as expected

[nikobockerman]

I wonder why the installation should be skipped in this scenario? I interpret the introduced reinstallGccVersionFromSource option as a request from the image user to install one specific GCC version. This condition here turns that option into a specifying a minimum GCC version instead of a specific version.

[Kaniska244]

The rationale behind this is that if the default GCC version is higher than that of the one specified in the template, then its better to retain the default one as it would already contain better features compared to the given GCC version in the template. Besides the actual issue was created to be able to use GCC 14 & 15 versions which were not available by default with the image.