gcc and libbackend.a

[ranjith kumar <ranjithproxy at gmail dot com>]

Hi,
 I am debugging  gcc-4.5.0 source code, built for C compiler only, using gdb.
 My question is  why we can not  keep break points on any of the  back
end functions(functions defined in libbackend.a library)???

I am explaining my question in detail:
   I downloaded gcc-4.5.0 and build it in objdir=OBJDIR and installed
into BIN directory.
when I run make install, it is copying xgcc file from OBJDIR to
BIN/usr/local/gcc.

This is the command by which xgcc is built:
gcc  -g -fkeep-inline-functions -DIN_GCC   -W -Wall -Wwrite-strings
-Wcast-qual -Wstrict-prototypes -Wmissin      g-prototypes
-Wmissing-format-attribute -pedantic -Wno-long-long
-Wno-variadic-macros -Wno-overlength-string      s
-Wold-style-definition -Wc++-compat -fno-common  -DHAVE_CONFIG_H  -o
xgcc gcc.o opts-common.o gcc-options. o
   gccspec.o intl.o prefix.o version.o driver-i386.o
../libcpp/libcpp.a   ../libiberty/libiberty.a .
./libdecnumber/libdecnumber.a


So in building xgcc it is not using libbackend.a library. I think this
is the reason why I am unable to keep breakpoints on any of the back
end's functions.right?
But why xgcc is not built by using libbackend.a library? From where
xgcc/gcc is getting the backend functions definitions?

Also what are cc,cc1-dummy files? They are built using libbackend.a library.

Thanks in advance.