add option --with-clang to configure the build system to use clang and clang++ instead of gcc and g++. Only use this option when the build target is using the gcc compiler.
add option --with-clang to configure the build system to use clang and clang++
instead of gcc and g++. Only use this option when the build target is using
the gcc compiler.


git-svn-id: ecbadac9c76e8cf640a0bca86f6bd796c98521e3@32567 27541ba8-7e3a-0410-8455-c3a389f83636

dawehner/root,dawehner/root,bbannier/ROOT,dawehner/root,bbannier/ROOT,bbannier/ROOT,bbannier/ROOT,dawehner/root,bbannier/ROOT,dawehner/root,dawehner/root,bbannier/ROOT,dawehner/root,bbannier/ROOT,dawehner/root