x86 vDSO: vdso32 build

x86 vDSO: vdso32 build

This builds the 32-bit vDSO images in the arch/x86/vdso subdirectory.
Nothing uses the images yet, but this paves the way for consolidating
the vDSO build logic all in one place.  The new images use a linker
script sharing the layout parts from vdso-layout.lds.S with the 64-bit
vDSO.  A new vdso32-syms.lds is generated in the style of vdso-syms.lds.

Signed-off-by: Roland McGrath <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>