builder,pref: Allow thirdparty objects compilation with CPP compiler

[lenaing]

Hi,

As I was working on a binding for an external CPP library, I was hit by:

• not finding CPP files to compile
• standard C compilations flags that depends on wether we are compiling a C file or a CPP one

This PR enable one to bind and build such binding, by keeping the #flag @VEXEROOT/thirdparty/path/to/object.o compatibilty.

Kind regards,

🤖 Generated by Copilot at 231859a

This pull request adds support for custom C++ compilers in V and enables compiling third party modules that use C++ code. It modifies the Preferences struct, the cc.v and pref.v files, and adds a -c++ flag to choose the compiler.

🤖 Generated by Copilot at 231859a

• Add support for C++ files in third party modules (link, link, link, link, link, link, link, link, link, link, link)

• Define constants for C and C++ standards in vlib/v/builder/cc.v (link)
• Remove hard-coded C standard flags from C compiler options (link)
• Add C standard flags to source-specific arguments based on OS and no_std preference (link)
• Pass file type argument to thirdparty_object_args function (link, link)
• Add C or C++ standard flags to thirdparty_object_args function based on OS, no_std preference, and file type (link)
• Check if guessed C file exists and set file type flag accordingly in build_thirdparty_obj_file function (link)
• Switch to C++ compiler if file type is C++ in build_thirdparty_obj_file function (link)
• Set default C++ compiler if not specified by user in default_ccompiler function in vlib/v/pref/default.v (link)
• Add default_cpp_compiler function to Preferences struct in vlib/v/pref/default.v (link)
• Add cppcompiler field to Preferences struct in vlib/v/pref/pref.v (link)
• Add -c++ option to command line parser in vlib/v/pref/pref.v (link)

[spytheman]

Good work. It does need a small test to keep it from regressing. I'll add it asap.