[Bug bootstrap/55961] [4.8 Regression] system.h includes gmp.h but system.h is included for build and not just target

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55961

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2013-01-14 16:05:48 UTC ---
We run configure for the build system in a subdirectory, when build != 
host.

# auto-host.h is the file containing items generated by autoconf and is
# the first file included by config.h.
# If host=build, it is correct to have bconfig include auto-host.h
# as well.  If host!=build, we are in error and need to do more 
# work to find out the build config parameters.
if test x$host = x$build
then
        build_auto=auto-host.h
else
        # We create a subdir, then run autoconf in the subdir.
        # To prevent recursion we set host and build for the new
        # invocation of configure to the build for this invocation
        # of configure. 
[...]