suppress unwanted warnings when configuring with clang
coding style warnings enabled by default in clang have long been a
source of spurious questions/bug-reports. since clang provides a -w
that behaves differently from gcc's, and that lets us enable any
warnings we may actually want after turning them all off to start with
a clean slate, use it at configure time if clang is detected.
diff --git a/configure b/configure
index a272896..4359882 100755
--- a/configure
+++ b/configure
@@ -495,6 +495,13 @@
fi
#
+# GCC defines -w as overriding any -W options, regardless of order, but
+# clang has a bunch of annoying warnings enabled by default and needs -w
+# to start from a clean slate. So use -w if building with clang.
+#
+test "$cc_family" = clang && tryflag CFLAGS_AUTO -w
+
+#
# Even with -std=c99, gcc accepts some constructs which are constraint
# violations. We want to treat these as errors regardless of whether
# other purely stylistic warnings are enabled -- especially implicit