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ref #6695

fixes #6529

otherwise it's non-trivial to build modules. and seems to be the
only sane way to setup flags so that the kbuild tests get it right
for stack protector tests.

KCFLAGS is too late for gcc flags detection logic. So embed the
-fno-pie flag directly to CC. This fixes the error:
Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong not supported by compiler

fixes #5191
fixes #6486

fixes #6425

ref #6071
upstream: https://forums.grsecurity.net/viewtopic.php?f=3&t=4441

fixes #5886