Add -Wno-extended-offsetof for clang-3 #924

Job	Run time
Package builder app	5s
Clean up previous branch jobs	6s
Unit Tests	4s
cross_compile (linux-armv6)	10m 16s
cross_compile (linux-armv7)	10m 5s
cross_compile (linux-armv8)	10m 12s
release_notes (aws-crt-python)	44s
compilers (clang-9)	1m 15s
release_notes (aws-iot-device-sdk-python-v2)	3s
compilers (clang-10)	37s
Sanity Test (ubuntu-22.04)	2m 31s
compilers (clang-11)	43s
Sanity Test (macos-11)	2m 55s
compilers (gcc-7)	29s
Sanity Test (macos-12)	3m 22s
compilers (gcc-8)	36s
compilers (gcc-9)	27s
Sanity Test (windows-2022)	3m 13s
compilers (gcc-10)	30s
compilers (gcc-11)	41s
aws-c-cal (manylinux1-x86)	2m 32s
downstream (aws-c-mqtt)	11m 32s
aws-c-cal (manylinux1-x64)	2m 18s
downstream (aws-c-http)	4m 7s
aws-c-cal (manylinux2014-x86)	2m 53s
swift (swift-5-ubuntu-x64)	41s
downstream (aws-crt-python)	4m 21s
aws-c-cal (manylinux2014-x64)	2m 43s
swift (swift-5-centos-x64)	39s
downstream (aws-crt-cpp)	6m 54s
aws-c-cal (manylinux2014-aarch64)	23m 16s
swift (swift-5-al2-x64)	38s
downstream (aws-crt-java)	6m 22s
aws-c-cal (musllinux-1-1-aarch64)	25m 47s
downstream (aws-crt-nodejs)	7m 8s
aws-c-cal (musllinux-1-1-x64)	2m 34s
std-compat (gcc-8, c++11)	7m 40s
std-compat (gcc-8, c++14)	5m 30s
std-compat (gcc-8, c++17)	7m 16s
std-compat (gcc-8, c++2a)	6m 6s
std-compat (clang-9, c++11)	6m 3s
std-compat (clang-9, c++14)	5m 13s
std-compat (clang-9, c++17)	6m 53s
std-compat (clang-9, c++2a)	6m 22s
All Sanity Tests passed	1s
	3h 24m 23s

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