vmlinux.lds.h: Keep .ctors.* with .ctors

Under some circumstances, the compiler generates .ctors.* sections. This
is seen doing a cross compile of x86_64 from a powerpc64el host:

x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/trace_clock.o' being
placed in section `.ctors.65435'
x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/ftrace.o' being
placed in section `.ctors.65435'
x86_64-linux-gnu-ld: warning: orphan section `.ctors.65435' from `kernel/trace/ring_buffer.o' being
placed in section `.ctors.65435'

Include these orphans along with the regular .ctors section.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 83109d5d ("x86/build: Warn on orphan section placement")
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20201005025720.2599682-1-keescook@chromium.org

include/asm-generic/vmlinux.lds.h

@@ -701,6 +701,7 @@
 #ifdef CONFIG_CONSTRUCTORS
 #define KERNEL_CTORS()	. = ALIGN(8);			   \
 			__ctors_start = .;		   \
+			KEEP(*(SORT(.ctors.*)))		   \
 			KEEP(*(.ctors))			   \
 			KEEP(*(SORT(.init_array.*)))	   \
 			KEEP(*(.init_array))		   \