x86/unwind/orc: Fix ORC unwind table alignment

The .orc_unwind section is a packed array of 6-byte structs.  It's
currently aligned to 6 bytes, which is causing warnings in the LLD
linker.

Six isn't a power of two, so it's not a valid alignment value.  The
actual alignment doesn't matter much because it's an array of packed
structs.  An alignment of two is sufficient.  In reality it always gets
aligned to four bytes because it comes immediately after the
4-byte-aligned .orc_unwind_ip section.

Fixes: ee9f8fce99 ("x86/unwind: Add the ORC unwinder")
Reported-by: Nick Desaulniers <[email protected]>
Reported-by: Dmitry Golovin <[email protected]>
Reported-by: Sedat Dilek <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Sedat Dilek <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
Link: https://github.com/ClangBuiltLinux/linux/issues/218
Link: https://lkml.kernel.org/r/d55027ee95fe73e952dcd8be90aebd31b0095c45.1551892041.git.jpoimboe@redhat.com

include/asm-generic/vmlinux.lds.h

@@ -733,7 +733,7 @@
 		KEEP(*(.orc_unwind_ip))					\
 		__stop_orc_unwind_ip = .;				\
 	}								\
-	. = ALIGN(6);							\
+	. = ALIGN(2);							\
 	.orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {		\
 		__start_orc_unwind = .;					\
 		KEEP(*(.orc_unwind))					\