m68knommu: align BSS section to 4-byte boundaries

The kernel start up code for all of the nommu m68k types expects the BSS
section to be on a 4-byte boundary, and to be a whole number of 32bit
words. The BSS initialization loop sets 32bit sized quantities and has
no provision for odd or unaligned accesses.

The alignment and size of the BSS has historically worked out to be 4-byte
aligned and sized - although no explicit alignment or size was specified in
the linker script. So the BSS zeroing code worked as expected.

A problem was first observed after commit 7273ad2b ("kbuild: link lib-y
objects to vmlinux forcibly when CONFIG_MODULES=y"). Some kernel builds,
depending on exact configuration, then tended to generate even sized BSS
sections - which is valid on m68k - but our BSS init code could not handle
properly.

The simplest and smallest solution is to align and size the BSS
appropriately.
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>

arch/m68k/kernel/vmlinux-nommu.lds

@@ -82,7 +82,7 @@ SECTIONS {
 		__init_end = .;
 	}
 
-	BSS_SECTION(0, 0, 0)
+	BSS_SECTION(4, 0, 4)
 
 	_end = .;