gcc build error: undefined _Unwind_Ptr

I have tried on build both gcc-4.6.2 and gcc-4.6.1 and failed.  Here is the error:

In file included from ../../.././libgcc/../gcc/unwind-dw2.c:35:0:
../../.././libgcc/../gcc/unwind-pe.h:101:1: error: unknown type name '_Unwind_Ptr'

Solution: rename the first unwind.h to another name and there should be another unwind.h which is good for building gcc.  The cause is the installation of libunwind which is claimed to be cleaner than gcc’s unwind but defined different/less prototypes.