csu: Add .note.ABI-tag and .note.GNU-stack

csu: Add .note.ABI-tag and .note.GNU-stack

For all arches except sparc, gcc emits the section directive for the
following struct with a PROGBITS type.  However, newer versions of binutils
(after 2.16.90) require the section to be of NOTE type, to guarantee that
the .note.ABI-tag section correctly ends up in the first page of the final
executable.

Unfortunately, there is no clean way to tell gcc to use another section
type, so this C file (or the C file that includes it) must be compiled in
multiple steps:

- Compile the .c file to a .s file.
- Edit the .s file to change the 'progbits' type to 'note', for the section
  directive that defines the .note.ABI-tag section.
- Compile the .s file to an object file.

These steps are done in the invididual Makefiles for each applicable arch.

Taken-from: FreeBSD SVN 217375 (13 JAN 2011)

On i386 crtn.S:
Keep the stack aligned to a 16 byte boundary when calling init functions
so that we don't cause a bus error if they start storing SSE math stuff
on the stack.

Taken-from: FreeBSD SVN 146369 (19 MAY 2005)