Revert "bitbake.conf: Start to separate out gcc definition"

This reverts commit a3ae3e9.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Author: rpurdie

meta/conf/bitbake.conf

@@ -841,8 +841,7 @@ include conf/licenses.conf
 require conf/sanity.conf
 include conf/bblock.conf
 
-TOOLCHAIN ??= "gcc"
-require toolchain/${TOOLCHAIN}.inc
+require toolchain/gcc.inc
 require toolchain/build-gcc.inc
 
 ##################################################################