libc/newlib: Canadian baremetal builds require core pass-1

Can safely skip the core pass-1 for normal baremetal builds,
but when building a canadian baremetal, the repair_cc
functionality (GCC_FOR_TARGET) in gcc.sh will force the
core pass-2 to attempt to build gcc and libgcc without a
${CT_TARGET}-gcc existing, causing a failure on
${CT_TARGET}-gcc -dumpspecs > tmp-specs

Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>