kasan patches

These patches are needed for kasan+clang support. I confirmed they apply cleanly in order (top to bottom):

4.9: commit c5caf21ab0cf8 ("kasan: turn on -fsanitize-address-use-after-scope") commit 0e410e158e5b ("kasan: don't emit builtin calls when sanitization is off")

4.4: commit c5caf21ab0cf8 ("kasan: turn on -fsanitize-address-use-after-scope")

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0e410e158e5b is the one I'm interested in. Looks like it landed in 4.16, and got backported to 4.14-stable.

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c5caf21ab0cf8 depends on c6d308534aef6 ("UBSAN: run-time undefined behavior sanity checker"), and I don't want to bring in all of UBSAN to 4.4. I'll send a patch for 0e410e158e5b.