Relax constraints on Machine_Attribute argument types:

    Relax constraints on Machine_Attribute argument types:
        * sem_prag.adb (Check_Arg_Is_Static_Expression): Allow for
        missing type.
        (Analyze_Attribute, case Machine_Attribute): Allow any type for
        arg 3.
        * gcc-interface/decl.c (prepend_attributes): Accept static
        expressions of any type as attribute arguments, not only string
        literals.
        * gnat_rm.texi (pragma Machine_Attribute section): Adjust to
        reflect the relaxation of the restriction on the Info argument type.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@148589 138bc75d-0d04-0410-961f-82ee72b054a4