The arduino ide allows libraries to be include in sketch programs using #include <libFolderName>. In normal programing this would refer to a <LibFileName.h> file in a library path. This does not work well for visual studio intellisense or build/compile.

Visual Micro solves this problem as follows

The #include in a .pde file is ignored and has no relevence in visual studio. The sole purpose of the #include library in a .pde maintains compatibility with the arduino ide

Visual Micro attaches the library files as files to a sketch project. When any code file is attached to a visual studio project it automatically is included in intellisense

When you add an arduino library to a visual studio project, Visual Micro modifies _vsaddin\include_libs.h with the path to the library.h file

The _vsaddin\include_libs.h file is also rebuilt when you build or compile a visual studio sketch project. This ensures any libraries you have manually attached to the project are included

Summary

The _vsaddin\include_libs.h is automatically maintained by visual micro and is used by the avr-gcc compiler to resolve references to arduino libraries