This is xnu-8019. See this file in:
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#BEGIN	Machine dependent Makefile fragment for x86_64
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#
# XXX: CFLAGS
#
CWARNFLAGS   = $(CWARNFLAGS_STD) -Wshorten-64-to-32 -Wimplicit-int-conversion
CXXWARNFLAGS = $(CXXWARNFLAGS_STD) -Wshorten-64-to-32 -Wimplicit-int-conversion

mkext.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
inet_ntop.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
inet_pton.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
log.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
z_crc32.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
deflate.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
trees.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
trees.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
corecrypto_sha1.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
corecrypto_md5.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
corecrypto_aes.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
kxld_sym.o_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
OSUnserializeXML.cpo_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion
OSUnserialize.cpo_CWARNFLAGS_ADD += -Wno-shorten-64-to-32 -Wno-implicit-int-conversion

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#END	Machine dependent Makefile fragment for x86_64
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