hai have gcc compilation error during gcc installtion in linuxfromscratch:
loading cache ./config.cache
checking host system type... i686-pc-linux-gnu
checking target system type... i686-pc-linux-gnu
checking build system type... i686-pc-linux-gnu
checking for a BSD compatible install... (cached) /tools/bin/install -c
checking whether ln works... (cached) yes
checking whether ln -s works... (cached) yes
checking for gcc... (cached) gcc
checking whether the C compiler (gcc ) works... yes
checking whether the C compiler (gcc ) is a cross-compiler... no
checking whether we are using GNU C... (cached) yes
checking whether gcc accepts -g... (cached) yes
checking for gnatbind... no
checking whether compiler driver understands Ada... (cached) no
checking how to compare bootstrapped objects... (cached) cmp --ignore-initial=16 $$f1 $$f2
checking for correct version of gmp.h... no
*** This configuration is not supported in the following subdirectories:
target-libada target-libgfortran target-libffi target-boehm-gc target-zlib target-libjava zlib fastjar target-libobjc
(Any other directories should still work fine.)
checking for bison... no
checking for bison... no
checking for byacc... no
checking for yacc... no
checking for gm4... (cached) m4
checking for flex... no
checking for flex... no
checking for lex... no
checking for makeinfo... (cached) makeinfo
*** removing build-i686-pc-linux-gnu/libiberty/Makefile to force reconfigure
*** removing build-i686-pc-linux-gnu/fixincludes/Makefile to force reconfigure
*** removing intl/Makefile to force reconfigure
*** removing libiberty/Makefile to force reconfigure
*** removing libcpp/Makefile to force reconfigure
*** removing fixincludes/Makefile to force reconfigure
*** removing gcc/Makefile to force reconfigure
checking for i686-pc-linux-gnu-ar... no
checking for ar... (cached) ar
checking for i686-pc-linux-gnu-as... no
checking for as... (cached) as
checking for i686-pc-linux-gnu-dlltool... no
checking for dlltool... (cached) dlltool
checking for i686-pc-linux-gnu-ld... (cached) /tools/lib/gcc/i686-pc-linux-gnu/4.0.3/../../../../i686-pc-linux-gnu/bin/ld
checking for i686-pc-linux-gnu-nm... no
checking for nm... (cached) nm
checking for i686-pc-linux-gnu-ranlib... no
checking for ranlib... (cached) ranlib
checking for i686-pc-linux-gnu-windres... no
checking for windres... (cached) windres
checking for i686-pc-linux-gnu-objcopy... no
checking for objcopy... (cached) objcopy
checking for i686-pc-linux-gnu-objdump... no
checking for objdump... (cached) objdump
checking for i686-pc-linux-gnu-ar... no
checking for ar... (cached) ar
checking for i686-pc-linux-gnu-as... no
checking for as... (cached) as
checking for i686-pc-linux-gnu-dlltool... no
checking for dlltool... (cached) dlltool
checking for i686-pc-linux-gnu-ld... no
checking for ld... (cached) ld
checking for i686-pc-linux-gnu-nm... no
checking for nm... (cached) nm
checking for i686-pc-linux-gnu-ranlib... no
checking for ranlib... (cached) ranlib
checking for i686-pc-linux-gnu-windres... no
checking for windres... (cached) windres
checking whether to enable maintainer-specific portions of Makefiles... no
checking if symbolic links between directories work... (cached) yes
creating ./config.status
creating Makefile
please answer how to compile gcc-4.0.5

In file included from ../../gcc-4.0.3/gcc/crtstuff.c:64:
../../gcc-4.0.3/gcc/tsystem.h:90:19: error: stdio.h: No such file or directory
../../gcc-4.0.3/gcc/tsystem.h:93:23: error: sys/types.h: No such file or directory
../../gcc-4.0.3/gcc/tsystem.h:96:19: error: errno.h: No such file or directory
../../gcc-4.0.3/gcc/tsystem.h:103:20: error: string.h: No such file or directory
../../gcc-4.0.3/gcc/tsystem.h:104:20: error: stdlib.h: No such file or directory
../../gcc-4.0.3/gcc/tsystem.h:105:20: error: unistd.h: No such file or directory
In file included from /sources/gcc-builts1/gcc/include/syslimits.h:7,
from /sources/gcc-builts1/gcc/include/limits.h:11,
from ../../gcc-4.0.3/gcc/tsystem.h:108,
from ../../gcc-4.0.3/gcc/crtstuff.c:64:
/sources/gcc-builts1/gcc/include/limits.h:122:61: error: limits.h: No such file or directory
In file included from ../../gcc-4.0.3/gcc/crtstuff.c:64:
../../gcc-4.0.3/gcc/tsystem.h:111:18: error: time.h: No such file or directory
make[1]: *** [crtbegin.o] Error 1
make[1]: Leaving directory `/sources/gcc-builts1/gcc'
make: *** [all-gcc] Error 2

Cant understand why you chose this thread to post your query (2 times??),
once ./configure is done without error
then
>make
>su
pwd
>make install

That would be a good example of not posting in the right forum.