build: comment on why we're not adopting certain flake8 rules

Simplify the list of ignored warnings now that we only have two left,
and document why we're not honouring them.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

build-aux/syntax-check.mk

@@ -882,13 +882,17 @@ sc_require_enum_last_marker:
 	  { echo '$(ME): enum impl needs _LAST marker on second line' 1>&2; \
 	    exit 1; } || :
 
-# Validate many python style rules
-FLAKE8_LINE_LENGTH = E501
-FLAKE8_WARNINGS = W504
-
-FLAKE8_IGNORE = $(FLAKE8_LINE_LENGTH),$\
-		$(FLAKE8_WARNINGS) \
-		$(NULL)
+# We're intentionally ignoring a few warnings
+#
+# E501: Force breaking lines at < 80 characters results in
+# some really unnatural code formatting which harms
+# readability.
+#
+# W504: Knuth code style requires the operators "or" and "and" etc
+# to be at the start of line in a multi-line conditional.
+# This the opposite to what is normal libvirt practice.
+#
+FLAKE8_IGNORE = E501,W504
 
 sc_flake8:
 	@if [ -n "$(FLAKE8)" ]; then \