selftests: kvm: Fix libkvm build error

Fix the following build error from "make TARGETS=kvm kselftest":

libkvm.a(assert.o): relocation R_X86_64_32 against `.rodata.str1.1' can not be used when making a PIE object; recompile with -fPIC

This error is seen when build is done from the main Makefile using
kselftest target. In this case KBUILD_CPPFLAGS and CC_OPTION_CFLAGS
are defined.

When build is invoked using:

"make -C tools/testing/selftests/kvm" KBUILD_CPPFLAGS and CC_OPTION_CFLAGS
aren't defined.

There is no need to pass in KBUILD_CPPFLAGS and CC_OPTION_CFLAGS for the
check to determine if --no-pie is necessary, which is the case when these
two aren't defined when "make -C tools/testing/selftests/kvm" runs.

Fix it by simplifying the no-pie-option logic. With this change, both
build variations work.

"make TARGETS=kvm kselftest"
"make -C tools/testing/selftests/kvm"

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>