Fix initializer_constant_valid_p_1 TYPE_PRECISION use

Fix initializer_constant_valid_p_1 TYPE_PRECISION use

initializer_constant_valid_p_1 is letting through all conversions
of float vector types that have the same number of elements but
that's of course not valid.  The following restricts the code
to scalar floating point types as was probably intended (only
scalar integer types are handled as well).

	* varasm.cc (initializer_constant_valid_p_1): Only
	allow conversions between scalar floating point types.