Turn off debug information in C extension

Previously, pydantic used the default Python CFLAGS which include `-g`
(debug level 2). This is good for debugging at the C level, but it
significantly increases the size of the C extension shared library, and
is probably not needed by the vast majority of pydantic users. Thus, it
seems a better tradeoff to turn debug info off.

This can be overridden when building pydantic from source (not from PyPI
wheel) by using `CFLAGS='-O3 -g'`.

This change reduces the pydantic binary on cp310-linux-x86_64 from 31MB
(12MB wheel) to 8.9MB (3MB wheel).

Fixes pydantic#2276

setup.py

@@ -84,7 +84,7 @@ def extra(self):
             compiler_directives['linetrace'] = True
         # Set CFLAG to all optimizations (-O3)
         # Any additional CFLAGS will be appended. Only the last optimization flag will have effect
-        os.environ['CFLAGS'] = '-O3 ' + os.environ.get('CFLAGS', '')
+        os.environ['CFLAGS'] = '-O3 -g0' + os.environ.get('CFLAGS', '')
         ext_modules = cythonize(
             'pydantic/*.py',
             exclude=['pydantic/generics.py'],