libiberty is not installed anymore, but its header file still is

[Nikos Chantziaras]

GCC does not install libiberty anymore.  This commit has disabled it:

http://gcc.gnu.org/viewcvs?view=revision&revision=175560

However, programs that were previously making use of functions like 
vasprintf() compile just fine and only fail at link time.  This is 
because libiberty.h is still installed by GCC.

Functions that are not available for the user shouldn't have any 
prototypes.  Can this be considered as a GCC bug?