chore(profiling): explicitly set or clear NDEBUG for memalloc extension (#13218)

The memalloc C extension has debug assert statements. We want them off
by default in case they guard a costly call we wouldn't normally want to
happen. Depending on how the CPython interpreter running setup.py was
built, we may already get -DNDEBUG via the CFLAGS from sysconfig, which
disables asserts. See the [setuptools
docs](https://setuptools.pypa.io/en/latest/userguide/ext_modules.html#compiler-and-linker-options).

But rather than rely on that, make sure that asserts
are explicitly disabled for normal builds and explicitly enabled for
debug builds.

Author: nsrip-dd

setup.py

@@ -614,7 +614,14 @@ def get_exts_for(name):
                 "ddtrace/profiling/collector/_memalloc_reentrant.c",
             ],
             extra_compile_args=(
-                debug_compile_args + ["-D_POSIX_C_SOURCE=200809L", "-std=c11"] + fast_build_args
+                debug_compile_args
+                # If NDEBUG is set, assert statements are compiled out. Make
+                # sure we explicitly set this for normal builds, and explicitly
+                # _unset_ it for debug builds in case the CFLAGS from sysconfig
+                # include -DNDEBUG
+                + (["-DNDEBUG"] if not debug_compile_args else ["-UNDEBUG"])
+                + ["-D_POSIX_C_SOURCE=200809L", "-std=c11"]
+                + fast_build_args
                 if CURRENT_OS != "Windows"
                 else ["/std:c11"]
             ),