[Bug bootstrap/87146] New: ubsan bootstrap with non-gcc compiler fails

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87146

            Bug ID: 87146
           Summary: ubsan bootstrap with  non-gcc compiler fails
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: bootstrap
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
  Target Milestone: ---

This bootstrap configure line works fine:

../trunk/configure --prefix=/home/dcb/gcc/results.263945.ubsan \
        --with-build-config=bootstrap-ubsan \
        --disable-multilib \
        --disable-werror \
        --enable-checking=release \
        --enable-languages=c,c++,fortran

This doesn't

CC="/home/dcb/llvm/clang601/bin/clang -Wall" \
CXX="/home/dcb/llvm/clang601/bin/clang++ -Wall" \
../trunk/configure --prefix=/home/dcb/gcc/results.263945.ubsan \
        --with-build-config=bootstrap-ubsan \
        --disable-multilib \
        --disable-werror \
        --enable-checking=release \
        --enable-languages=c,c++,fortran

failing at the bootstrap compare 

Comparing stages 2 and 3
Bootstrap comparison failure!
fixincludes/fixfixes.o differs
gcc/ira-conflicts.o differs
gcc/gcc.o differs

gcc revision is 263945.

Should I wait for upcoming clang 7.0 or is there something
special about a non-gcc compiler bootstrap ?