Support special syntax for compilation and launch

[andreeis]

Will split later into more items if needed. Dumping all here for now.

Compilation

• cl.exe: /DMyDefine1=Val1,MyDefine2=Val2
• wrappers (cl.cmd)
• cl, lib and link: @file.rsp (response files)
• account for unusual or very old source file extensions (.c++, .C). hpp?
• conflicts analysis for switches that impact IntelliSense: /TC with /TP, /D and /U

Launch

• binary target invoked via "cmd -c", "start cmd", "source", "bash", conditioned by "@if (not) exist" ... etc ...

[andreeis]

Adding here flags that compilers may read from environment variables (like cl.exe reads CL, INCLUDE, lib.exe reads LIB, link.exe reads LINK, ... etc ...).

Read comment #444 (comment) about interesting scenario of make variables as another alternative source of include/defines/switches info.