kvm: Fix Nix build failure by moving -fno-stack-protector to CFLAGS

Nix and some Buildroot configs have the problem shown below.

gcc -I/home/rich/kernel/ltp/testcases/kernel/kvm/include -DCOMPILE_PAYLOAD -ffreestanding -O2 -Wall -fno-asynchronous-unwind-tables -mno-mmx\
 -mno-sse -fno-pie -c -o lib_guest.o lib_guest.c
as  -c -o bootstrap_x86_64.o bootstrap_x86_64.S
gcc -I/home/rich/kernel/ltp/testcases/kernel/kvm/include -DCOMPILE_PAYLOAD -ffreestanding -O2 -Wall -fno-asynchronous-unwind-tables -mno-mmx\
 -mno-sse -fno-pie -c -o lib_x86.o lib_x86.c
gcc -I/home/rich/kernel/ltp/testcases/kernel/kvm/include -I../../../include -I../../../include -I../../../include/old/ -DCOMPILE_PAYLOAD -ff\
reestanding -O2 -Wall -fno-asynchronous-unwind-tables -mno-mmx -mno-sse -fno-pie -nostdlib -Wl,--build-id=none -fno-stack-protector -z noexe\
cstack -no-pie -Wl,-T/home/rich/kernel/ltp/testcases/kernel/kvm/linker/x86_64.lds -o kvm_pagefault01-payload.elf kvm_pagefault01.c lib_guest\
.o bootstrap_x86_64.o lib_x86.o
/nix/store/inq79dwl8sz1ygmfbgsmg77i5cwmdjpz-binutils-2.40/bin/ld: lib_x86.o: in function `kvm_init_guest_vmcb':
lib_x86.c:(.text+0x7b3): undefined reference to `__stack_chk_fail'
collect2: error: ld returned 1 exit status
make: *** [Makefile:58: kvm_pagefault01-payload.o] Error 1

__stack_chk_fail is added to lib_x86.o which means that
-fstack-protector somehow gets added to the compilation of lib_x86.o.

Swapping -fno-stack-protector from the LD flags to the C flags ensures
it is disabled when compiling lib_x86.o.

Signed-off-by: Richard Palethorpe <[email protected]>
Reviewed-by: Martin Doucha <[email protected]>
Acked-by: Petr Vorel <[email protected]>

testcases/kernel/kvm/Makefile

@@ -8,8 +8,8 @@ include $(top_srcdir)/include/mk/testcases.mk
 ASFLAGS =
 CPPFLAGS += -I$(abs_srcdir)/include
 GUEST_CPPFLAGS = $(CPPFLAGS) -DCOMPILE_PAYLOAD
-GUEST_CFLAGS = -ffreestanding -O2 -Wall -fno-asynchronous-unwind-tables -mno-mmx -mno-sse
-GUEST_LDFLAGS = -nostdlib -Wl,--build-id=none -fno-stack-protector -z noexecstack
+GUEST_CFLAGS = -ffreestanding -O2 -Wall -fno-asynchronous-unwind-tables -fno-stack-protector -mno-mmx -mno-sse
+GUEST_LDFLAGS = -nostdlib -Wl,--build-id=none -z noexecstack
 GUEST_LDLIBS =
 KVM_LD ?= $(LD)