This reinstates and adjusts
commit e3d0fcbf7e.
* gnu/packages/patches/gcc-libiberty-printf-decl.patch: New file.
* gnu/packages/gcc.scm (gcc-5)[source]: Use it.
[patches]: Add "gcc-arm-bug-71399.patch".
(gcc): Switch to GCC-5.
* gnu/packages/commencement.scm (libstdc++-boot0): New variable.
(gcc-boot0)[inputs]: Add it.
(gcc-toolchain-4.9): Switch to GCC-4.9.
(gcc-toolchain-5): Switch to GCC-FINAL.
* gnu/local.mk (dist_patch_DATA): Add 'gcc-libiberty-printf-decl.patch'.
Ludovic Courtès