ifort error to find as and ld after installation gcc

Dear all,

I install gcc to my compiler directory:

~/compilers/gcc/gcc-5.3.0/bin/gcc

and I setup enviroment variables:

#-------------------------------------------------------------------------------

# GCC
#
export GCCVERSION=5.3.0
export GCCROOT=$HOME/compilers/gcc/gcc-$GCCVERSION
export LD_LIBRARY_PATH=$GCCROOT/lib64:$LD_LIBRARY_PATH
export C_INCLUDE_PATH=$GCCROOT/include/c++/$GCCVERSION:$C_INCLUDE_PATH
export C_INCLUDE_PATH=$HOME/compilers/gcc/source/gcc-5.3.0/x86_64-unknown-linux-gnu/libstdc++-v3/include/x86_64-unknown-linux-gnu:$C_INCLUDE_PATH
export INCLUDE=$HOME/compilers/gcc/source/gcc-5.3.0/x86_64-unknown-linux-gnu/libstdc++-v3/include/x86_64-unknown-linux-gnu:$INCLUDE
export PATH=$GCCROOT/bin:$PATH
#-------------------------------------------------------------------------------

export MPI_HOME=$HOME/program/mpich/mpich2-1.5-gfortran-$GCCVERSION

export PATH=$MPI_HOME/bin:$PATH
export INCLUDE=$MPI_HOME/include:$INCLUDE

But when I compile with ifort, it reported the following errors:

make[2]: Leaving directory `/home/user/program/zindo/zblas'
ifort -o zindo -traceback  -L./ control/zindo.o control/block1.o control/version.o control/libversion.o -Llib -lcontrol -lgeometry -lscf -lci -lspinorbit -lproperties -lclasic -lmndo -lgvb -llinear -llocalization -lsolvent -lmoments -linterfaces -lintegrals -lutil -lio -lalgebra -lzblas 
/home/user/compilers/gcc/gcc-5.3.0/bin/as: No such file or directory
/home/user/compilers/gcc/gcc-5.3.0/bin/ld: No such file or directory

However when I use "which" to locate the commad "as" and "ld", it can be found in the /usr/bin directory:

/usr/bin/as

/usr/bin/ld

Can anybody help me to solve this problem?