wmiconfig: don't export CC

* it also breaks multimachine sstate checksums:
  basehash changed from 130192c54799615343a7b84bd8132d7d to 41d55a7213b686ffcc52d1a5d515e444
  Variable CC value changed from
  arm-oe-linux-gnueabi-gcc  -march=armv7-a -fno-tree-vectorize      -mthumb-interwork -mfloat-abi=softfp -mfpu=neon -mtune=cortex-a8 --sysroot=/OE/shr-core/tmp-eglibc/sysroots/nokia900
  to
  arm-oe-linux-gnueabi-gcc  -march=armv7-a -fno-tree-vectorize      -mthumb-interwork -mfloat-abi=softfp -mfpu=neon -mtune=cortex-a8 --sysroot=/OE/shr-core/tmp-eglibc/sysroots/om-gta04

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>