Investigate the right set of C compilation flags

[lmazuel]

Right now, the setup.py passes "-g -O0" while CMake is passing "-O2"

x86_64-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -g -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -I/azure-uamqp-python/src/vendor/inc -I./src/vendor/azure-uamqp-c/deps/azure-c-shared-utility/pal/inc -I./src/vendor/azure-uamqp-c/deps/azure-c-shared-utility/inc -I./src/vendor/azure-uamqp-c/inc -I./src/vendor/azure-uamqp-c/deps/azure-c-shared-utility/pal/linux -I/azure-uamqp-python/env/include -I/usr/include/python3.6m -c uamqp/c_uamqp.c -o build/temp.linux-x86_64-3.6/uamqp/c_uamqp.o -g -O0 -std=gnu99 -fPIC

It's unclear without being a gcc expert in what optimisation levels the lib is actually compiled.

Wheel should be the most possible optimized for performance. We might consider adding a "DEBUG_COMPILE" env variable read by the setup.py to compile in debug mode for easier debugging. That's actually changing this line (necessary, maybe not sufficient):

"-DCMAKE_BUILD_TYPE=Release"

to

"-DCMAKE_BUILD_TYPE=Debug"