VisualGDB Makefiles
VisualGDB uses GNU Make to build its projects. Unlike other make-based IDEs that overwrite the makefiles on each build, VisualGDB generates the Makefile only once and only updates the source file list. You can safely edit the makefile, change build flags, specify additional options, even add new targets and rules - VisualGDB will not overwrite your settings.
For your convenience all build flags are separated from the makefile itself and stored in a file called flags.mak:
If you are familiar with GCC and want to customize the build settings, add new include directories or libraries, simply edit the flags.mak file and rebuild your project.
You can read more about editing the VisualGDB makefiles here.