Feature/VPP-2129-CPP-build-compatible

[mohammadmahdi255]

add cast to void * element:

• function return void *
• void * variable assignment
• handle void * in macros

add _ before keyword names in CPP that use as variable name in C like class, template, new
add cast for int to enum assignment
handle overflow cast like -1 to unsigned and ~0 currently

[dwallacelf]

Thank you so much for your interest! VPP takes patches at https://gerrit.fd.io/

git clone https://gerrit.fd.io/r/vpp

Using git review to contribute patches is recommended