Bypass the build targets generation

The extension is identifying all the makefile (build) targets by invoking "make -pRrq" and parsing the output. This is in general very quick even for large projects.

It may happen that this would take long, like for https://github.com/curl/curl.git, MONO, ZFS ... and others... which makes the configure step painfully long without any workaround to speed it up. Even if makefile.buildLog points somewhere and no make is invoked for parsing IntelliSense and Launch, still "make -pRrq" for finding targets will runs for a long time.

We need to provide a way to bypass this. Ideas:

• provide makefile.buildTargetsLog to parse a log provided by the user (who runs the command just once)
• or a boolean makefile.skipBuildTargets which would just skip this part (the extension always inserts 'all' so it's available and no target defined is equivalent to whatever target is considered default in the makefile)
• eventually with an array of string makefile.buildTargets to just define any build targets that are more relevant and are needed to be discovered. This would also be useful when the parser has bugs and misses to identify some of the build targets.

Start by tracing the configure step and the code that invokes "make -pRrq" to discover build targets. Compare how makefile.buildLog is handled for IntelliSense and Launch, then evaluate the proposed buildTargetsLog, skipBuildTargets, and buildTargets settings. Done means users can bypass or replace target discovery without breaking the extension's existing target behavior.