Build: Temporarily disable CRC CLMUL to silence OSS Fuzz

The code makes aligned 16-byte reads which may read up to 15 bytes
before the beginning or past the end of the buffer if the buffer
is misaligned. The unneeded bytes are then ignored. It cannot cross
page boundaries and thus cannot cause access violations.

This inherently trips address sanitizer which was already disabled
with __attribute__((__no_sanitize_address__)). However, it also
trips memory sanitizer if the extra bytes are uninitialized because
memory sanitizer doesn't see that those bytes then get ignored by
byte shuffling in the xmm registers.

The plan is to change the code so that all sanitizers pass but it's
not finished yet (performance shouldn't get worse) so as a temporary
measure to keep OSS Fuzz happy, the CLMUL CRC is now disabled even
though I think think the code is fine to use (and easy enough to review
the memory accesses in it too).

configure.ac

@@ -373,10 +373,12 @@ AM_CONDITIONAL(COND_ASM_X86, test "x$enable_assembler" = xx86)
 # CLMUL CRC #
 #############
 
+# FIXME: Turn it back on by default once the code has been revised
+# to not cause false alarms in sanitizers and thus in OSS Fuzz.
 AC_ARG_ENABLE([clmul-crc], AS_HELP_STRING([--disable-clmul-crc],
 		[Do not use carryless multiplication for CRC calculation
 		even if support for it is detected.]),
-	[], [enable_clmul_crc=yes])
+	[], [enable_clmul_crc=no])
 
 
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