After an aborted or clean build in a directory outside the gcc source tree, "make distclean" is supposed to remove all configuration information.  However, that is not the case for at least one target (pdf).  Using gcc-4.5.1 in my build directory (as a bash user):

$ cd gcc_build
$ ../gcc-4.5.1/configure
... # nothing unusual
$ make pdf
... # nothing unusual except pdf target seems to
    # result in LOTs of extra compilation

Come back the next day

$ export CC=/usr/local/bin/gcc-4.5.1
$ cd gcc_build
$ make distclean
$ ls -aCF
./  ../  fixincludes/
$ ../gcc-5.5.1/configure
... # nothing unusual
$ make pdf
make[1]: Entering directory `/usr/local/src/gcc_build'
make[2]: Entering directory `/usr/local/src/gcc_build'
make[2]: Leaving directory `/usr/local/src/gcc_build'
Configuring in ./fixincludes
configure: loading cache ./config.cache
configure: error: `CC' has changed since the previous run:
configure:   former value:  `gcc'
configure:   current value: `/usr/local/bin/gcc-4.5.1'
configure: error: in `/usr/local/src/gcc_build/fixincludes':
configure: error: changes in the environment can compromise the build
configure: error: run `make distclean' and/or `rm ./config.cache' and start over
make[1]: *** [configure-fixincludes] Error 1
make[1]: Leaving directory `/usr/local/src/gcc_build'
make: *** [do-pdf] Error 2