Rename `typename' in d-exp.y to avoid C++ reserved word

Rename `typename' in d-exp.y to avoid C++ reserved word

A recent patch introduced a variable named `typename' into d-exp.y,
and one of the --enable-with-cxx build slaves consequently failed to compile
this.  This patch simply adds an underscore into the name to avoid the
reserved word.

gdb/ChangeLog

	* d-exp.y (PrimaryExpression : TypeExp '.' IdentifierExp): Rename
	`typename' to `type_name' to avoid C++ reserved word.