This looks like there are some additional flags added to gcc calls (somewhere in the makefile, propably in CFLAGS line). If you have "-ansi" or "-std=c89" then C++ style comments will not work. Remove this flag and you should be fine.

This one looks like linking problem. It is not sufficient to only have a header for library included in source file for many libraries. You also have to link with that library. To do that you have to extend LIBS line in your makefile. For example if you want to use math functions you add #include <math.h> to your source file and LIBS=-lm to your makefile.

For many libraries the correct way to add their linking parameters is to use their config script. Try adding something similiar to `gst-config --cflags --libs` to your LIBS line. Hope this helps.