gcc-cross-initial: Reinstate limits.h generation fix

gcc-cross-initial: Reinstate limits.h generation fix

The removal of gcc-cross-intermediate inadvertently reintroduced a
problem with the limits.h file being incorrectly/inconsistently
generated.

http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=b0faebd1f07e1616004bd19664395932e7c2c48f
reverted part of:
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=c8815d2f21849deb9359706f54dc71490773415e

This reintroduces the protected sysroot ensuring the limits.h file is
always correctly generated. To reproduce the bug, build gcc-cross, then
rebuild gcc-cross-initial and it will reference the limits.h file from
gcc-cross in the sysroot.

(From OE-Core rev: 71854f5c8c6850ed37777cad21acc92fdbea32fc)

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