on how to compile gcc-4.6 correctly?

[Dennis]

Hi, all,
  I'm using gentoo distribution (including gmp/mpfr/mpc) that could compile
gcc-4.5.0, 4.5.1, and many snapshots correctly, including the recent one gcc-4.5-20100902,
but when I tried to compile gcc-4.6, any snapshot version, even recent gcc-4.6-20100904,
it always failed, the recent one failure compiling is:

../../gcc-4.6-20100904/gcc/c-decl.c: In function 'grokdeclarator':
../../gcc-4.6-20100904/gcc/c-decl.c:5533: warning: format not a string literal and no format arguments
../../gcc-4.6-20100904/gcc/c-decl.c: In function 'grokparms':
../../gcc-4.6-20100904/gcc/c-decl.c:6194: warning: format not a string literal and no format arguments
../../gcc-4.6-20100904/gcc/c-decl.c:7025:64: error: macro "ggc_alloc_cleared_lang_type" passed 1 arguments, but takes just 0
../../gcc-4.6-20100904/gcc/c-decl.c: In function 'finish_struct':
../../gcc-4.6-20100904/gcc/c-decl.c:7025: error: 'ggc_alloc_cleared_lang_type' undeclared (first use in this function)
../../gcc-4.6-20100904/gcc/c-decl.c:7025: error: (Each undeclared identifier is reported only once
../../gcc-4.6-20100904/gcc/c-decl.c:7025: error: for each function it appears in.)
../../gcc-4.6-20100904/gcc/c-decl.c:7308:62: error: macro "ggc_alloc_cleared_lang_type" passed 1 arguments, but takes just 0
../../gcc-4.6-20100904/gcc/c-decl.c: In function 'finish_enum':
../../gcc-4.6-20100904/gcc/c-decl.c:7308: error: 'ggc_alloc_cleared_lang_type' undeclared (first use in this function)
make: *** [c-decl.o] Error 1

I don't know what happened with that? When I search the 'ggc_alloc_cleared_lang_type' macro,
it really doesn't exist in the gcc-4.6-20100904 source, nor under /usr/include, so what is
that macro real dependency? the prerequisites page seems not help me,
http://gcc.gnu.org/install/prerequisites.html

Who have successfully build gcc-4.6 please help me, or have any clue, I have searched that ggc_alloc_cleared_lang_type
through google, but didn't find out any meaningful results,

please make sure have my email address on cc-list that I can receive your email, because I didn't subscribe such
high volume mailing list,

Thank you very much,

--
Dennis, from Singapore