In commit 92b2d0b ("fix fpga bootrom makefile") we should
have tested $(CC) to be not cc if we where not to set the
standard CC and OBJCOPY files.
This should fix building the bootrom and allow overriding
the CC/OBJCOPY when wanted.
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Co-authored-by: JeanRochCoulon <jean-roch.coulon@thalesgroup.com>