bootrom: fix CC/OBJCOPY setting (#2984)

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>

Author: bjdooks-ct

corev_apu/fpga/src/bootrom/Makefile

@@ -17,8 +17,10 @@ UART_BITRATE ?= 115200
 HAS_ETHERNET ?= 1
 endif
 
-CC ?= $(RISCV)/bin/${CROSSCOMPILE}gcc
-OBJCOPY ?= $(RISCV)/bin/$(CROSSCOMPILE)objcopy
+ifeq ($(CC),cc)
+  CC = $(RISCV)/bin/${CROSSCOMPILE}gcc
+  OBJCOPY = $(RISCV)/bin/$(CROSSCOMPILE)objcopy
+endif
 SED = sed
 PLATFORM_DEFINES = -DCLOCK_FREQUENCY=$(CLOCK_FREQUENCY) -DUART_BITRATE=$(UART_BITRATE) -D$(PLATFORM)