gcc: update to support compressed debug sections

Add a static build of zlib (1.2.8) required to support compressed debug
sections. Use static zlib for elfutils, binutils, and gcc.

Drop CXX and CXXCPP from elfutils, it's written only in C.

Add new options for GCC:
--enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-gnu-unique-object
--enable-plugin
--with-linker-hash-style=gnu
--enable-linker-build-id
--disable-dssi

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
gcc: fix $PATH; use 'eu-' program prefix for elfutils binaries

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>