PR middle-end/54860 - Make sure attributes hash table is created

PR middle-end/54860 - Make sure attributes hash table is created

On targets cris-elf, alpha and sparc (for instance) it can happen that
the attribute_tables variable is empty for fortran.  Thus
register_scoped_attributes (called by init_attributes) won't call
register_scoped_attributes, so the hash table member of
scoped_attributes is not created.

Later when we try to e.g, lookup an attribute by calling
lookup_scoped_attribute_spec, that NULL member hash table comes to
byte us as htab_find_with_hash crashes.

This patch fixes this by ensuring in register_scoped_attributes that
the hash table is created.

Tested on cris-elf, x86_64-unknown-linux-gnu against trunk and some
commenters on the bug bootstrapped it on alpha and sparc.

gcc/

	* attribs.c (register_scoped_attributes): Ensure the attribute
	hash table is created.

From-SVN: r192301