dev-python/lxml: avoid suppressing compiler warnings

By default, setupinfo.py injects `-w` to the CFLAGS passed down to
Extension objects. This obscures things we'd like to see. For example,
it prevents adding Modern C Porting flags.

Signed-off-by: Eli Schwartz <eschwartz93@gmail.com>
Closes: https://bugs.gentoo.org/917562
Signed-off-by: Michał Górny <mgorny@gentoo.org>

dev-python/lxml/lxml-4.9.3-r2.ebuild

@@ -76,6 +76,10 @@ python_prepare_all() {
 }
 
 python_compile() {
+	local DISTUTILS_ARGS=(
+		# by default it adds -w to CFLAGS
+		--warnings
+	)
 	tc-export PKG_CONFIG
 	distutils-r1_python_compile
 }