Richard enhanced the warning in Clang r312842

From https://build.chromium.org/p/chromium.fyi/builders/ClangToTLinux/builds/9074

FAILED: obj/third_party/libxml/libxml/xpath.o 
../../third_party/llvm-build/Release+Asserts/bin/clang -MMD -MF obj/third_party/libxml/libxml/xpath.o.d -DV8_DEPRECATION_WARNINGS -DUSE_UDEV -DUSE_AURA=1 -DUSE_PANGO=1 -DUSE_CAIRO=1 -DUSE_GLIB=1 -DUSE_NSS_CERTS=1 -DUSE_X11=1 -DFULL_SAFE_BROWSING -DSAFE_BROWSING_CSD -DSAFE_BROWSING_DB_LOCAL -DCHROMIUM_BUILD -DFIELDTRIAL_TESTING_ENABLED -DCR_CLANG_REVISION=\"312916\" -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -DCOMPONENT_BUILD -DNDEBUG -DNVALGRIND -DDYNAMIC_ANNOTATIONS_ENABLED=0 -DU_USING_ICU_NAMESPACE=0 -DU_ENABLE_DYLOAD=0 -DICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE -DUCHAR_TYPE=uint16_t -I../../third_party/libxml/linux -I../.. -Igen -I../../third_party/libxml/src/include -I../../third_party/libxml/linux/include -I../../third_party/icu/source/common -I../../third_party/icu/source/i18n -I../../third_party/zlib -fno-strict-aliasing --param=ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D__DATE__= -D__TIME__= -D__TIMESTAMP__= -funwind-tables -fPIC -pipe -B../../third_party/binutils/Linux_x64/Release/bin -pthread -fcolor-diagnostics -m64 -march=x86-64 -O2 -fno-ident -fdata-sections -ffunction-sections -fomit-frame-pointer -g2 -fvisibility=hidden -Wheader-hygiene -Wstring-conversion -Wtautological-overlap-compare -Werror -Wall -Wno-unused-variable -Wno-missing-field-initializers -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override -Wno-undefined-var-template -Wno-nonportable-include-path -Wno-address-of-packed-member -Wno-unused-lambda-capture -Wno-user-defined-warnings -Wno-enum-compare-switch -Wno-tautological-unsigned-zero-compare -Wno-pointer-sign -Wno-empty-body -Wno-tautological-pointer-compare -Wno-ignored-attributes -Wno-int-to-void-pointer-cast -Wno-incompatible-pointer-types -Wno-unused-function -DLIBXML_STATIC= -std=gnu11 --sysroot=../../build/linux/debian_jessie_amd64-sysroot -c ../../third_party/libxml/src/xpath.c -o obj/third_party/libxml/libxml/xpath.o
../../third_party/libxml/src/xpath.c:12420:28: error: comparison of two values with different enumeration types ('xmlElementType' and 'xmlXPathTypeVal') [-Werror,-Wenum-compare]
                    } else if (cur->type == type) {
                               ~~~~~~~~~ ^  ~~~~
1 error generated.




Let's see how widespread this is. If it's just that one, perhaps disabling the warning for libxml makes sense.