[U-Boot] [PATCH] If CONFIG_SANDBOX isn't defined the build fails in fw_env.c

[Peter Robinson]

In our Fedora builds we get the below errors if we build the following using 
a vanilla u-boot 2015.07rc2. I'm not sure if it's the best fix but it fixes
the build for rc2.

make HOSTCC="gcc $RPM_OPT_FLAGS" CROSS_COMPILE="" defconfig V=1 O=builds/
make HOSTCC="gcc $RPM_OPT_FLAGS" CROSS_COMPILE="" tools-all V=1 O=builds/

gcc -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Wp,-MD,tools/env/.fw_env.o.d -Itools/env -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -idirafterinclude -idirafter../include -idirafter../arch/sandbox/include -idirafter ../tools/env -DUSE_HOSTCC -DTEXT_BASE= -c -o tools/env/fw_env.o ../tools/env/fw_env.c
In file included from ../include/configs/sandbox.h:130:0,
                 from include/config.h:5,
                 from ../tools/env/fw_env.h:11,
                 from ../tools/env/fw_env.c:34:
../include/env_default.h:104:2: error: expected '}' before 'BOOT_TARGET_DEVICES_references_HOST_without_CONFIG_SANDBOX'
  CONFIG_EXTRA_ENV_SETTINGS
  ^
scripts/Makefile.host:108: recipe for target 'tools/env/fw_env.o' failed
make[2]: *** [tools/env/fw_env.o] Error 1

Regards,
Peter