re PR c++/2936 (gcc gives me an internal error when compiling mozilla with --enable-optimization="-O3")

cp:
	PR g++/2936
	* decl.c (finish_anon_union): Copy context.
	* optimize.c (remap_decl): Remap anonymous aggregate members too.
testsuite:
	* g++.old-deja/g++.other/optimize3.C: New file.

From-SVN: r42705