Hi,
This is a revamped expr.h flattening flattening patch rebased on
tree.h and tree-core.h flattening patch (r219402).
It depends upon the following patch to get committed.
https://gcc.gnu.org/ml/gcc-patches/2015-01/msg00565.html

Changes:
* Removed all includes except tree-core.h. Put includes required by
expr.h in a comment.
* Moved stmt.c, expmed.c prototypes to stmt.h, expmed.h respectively.
* Adjusted generator programs: genemit.c, gengtype.c, genopinit.c, genoutput.c.
* Did not put includes in gcc-plugin.h since expr.h cannot be included
by plugins
(putting them broke building a file in c-family/ since expr.h is not
allowed in front-ends)
* Affects java front-end (expr.h is allowed in java front-end).

Bootstrapped and tested on x86_64-unknown-linux-gnu with languages:
all,go,ada,jit
Built on all targets in config-list.mk with languages: all, go.
OK to commit ?

Thanks,
Prathamesh