ubsan: disable UBSAN_DIV_ZERO for clang

Building with UBSAN_DIV_ZERO with clang produces numerous fallthrough
warnings from objtool.

In the case of uncheck division, UBSAN_DIV_ZERO may introduce new
control flow to check for division by zero.

Because the result of the division is undefined, LLVM may optimize the
control flow such that after the call to __ubsan_handle_divrem_overflow
doesn't matter.  If panic_on_warn was set,
__ubsan_handle_divrem_overflow would panic.

The problem is is that panic_on_warn is run time configurable.  If it's
disabled, then we cannot guarantee that we will be able to recover
safely.  Disable this config for clang until we can come up with a
solution in LLVM.

Link: ClangBuiltLinux#1657
Link: llvm/llvm-project#56289
Link: https://lore.kernel.org/lkml/CAHk-=wj1qhf7y3VNACEexyp5EbkNpdcu_542k-xZpzmYLOjiCg@mail.gmail.com/
Reported-by: Sudip Mukherjee <[email protected]>
Suggested-by: Linus Torvalds <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Acked-by: Nathan Chancellor <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

lib/Kconfig.ubsan

@@ -84,6 +84,9 @@ config UBSAN_SHIFT
 config UBSAN_DIV_ZERO
 	bool "Perform checking for integer divide-by-zero"
 	depends on $(cc-option,-fsanitize=integer-divide-by-zero)
+	# https://github.com/ClangBuiltLinux/linux/issues/1657
+	# https://github.com/llvm/llvm-project/issues/56289
+	depends on !CC_IS_CLANG
 	help
 	  This option enables -fsanitize=integer-divide-by-zero which checks
 	  for integer division by zero. This is effectively redundant with the