build: configure: only use my usual warning flags

I don't care about having my variable declarations at the beginning of
my functions, if I'm using C99 I should be able to use its features.

src/parse/local.am

@@ -24,4 +24,5 @@ BUILT_SOURCES += \
 # Remove problematic warnings from generated files
 libparse_a_CFLAGS = \
     -Wno-switch-default \
+    -Wno-unused-function \
     $(NULL)