This is xnu-8019. See this file in:
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#BEGIN	Machine dependent Makefile fragment for arm
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#
# Diagnostic opt-outs.  We need to make this list empty.
#
# DO NOT ADD MORE HERE.
#
# -Wno-implicit-int-conversion
OSSpinLock.o_CWARNFLAGS_ADD += -Wno-implicit-int-conversion
# -Wno-shorten-64-to-32
OSArray.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSDictionary.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSKextVersion.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSOrderedSet.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSRuntime.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSSerializeBinary.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSString.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32
OSSymbol.cpo_CXXWARNFLAGS_ADD += -Wno-shorten-64-to-32

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#END	Machine dependent Makefile fragment for arm
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