[efi] Allow building with non-system libbfd

On Mac OS X, it is necessary to build binutils manually; the system
does not provide bfd.h or the libbfd or libiberty libraries.

Originally-fixed-by: Joshua Oreman <oremanj@rwcr.net>

src/Makefile

 EFIROM		:= ./util/efirom
 ICCFIX		:= ./util/iccfix
 DOXYGEN		:= doxygen
+BINUTILS_DIR	:= /usr
+BFD_DIR		:= $(BINUTILS_DIR)
 
 ###############################################################################
 #

src/Makefile.housekeeping

 #
 # The EFI image converter
 #
+ELF2EFI_CFLAGS	:= -I$(BINUTILS_DIR)/include -I$(BFD_DIR)/include \
+		   -idirafter include -L$(BINUTILS_DIR)/lib -L$(BFD_DIR)/lib \
+		   -lbfd -liberty -lz
+
 $(ELF2EFI32) : util/elf2efi.c $(MAKEDEPS)
 	$(QM)$(ECHO) "  [HOSTCC] $@"
-	$(Q)$(HOST_CC) -DMDE_CPU_IA32 -idirafter include -O2 \
-		-o $@ $< -lbfd -liberty
+	$(Q)$(HOST_CC) $(ELF2EFI_CFLAGS) -DMDE_CPU_IA32 -O2 -o $@ $<
 CLEANUP += $(ELF2EFI32)
 
 $(ELF2EFI64) : util/elf2efi.c $(MAKEDEPS)
 	$(QM)$(ECHO) "  [HOSTCC] $@"
-	$(Q)$(HOST_CC) -DMDE_CPU_X64 -idirafter include -O2 \
-		-o $@ $< -lbfd -liberty
+	$(Q)$(HOST_CC) $(ELF2EFI_CFLAGS) -DMDE_CPU_X64 -O2 -o $@ $<
 CLEANUP += $(ELF2EFI64)
 
 $(EFIROM) : util/efirom.c $(MAKEDEPS)