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.

configure.ac

@@ -31,7 +31,11 @@ AC_PROG_CC_C99
 AC_PROG_CC_STDC
 
 # Warnings
-AX_COMPILER_FLAGS([], [], [], [-Wall -Wextra -pedantic])
+AX_APPEND_COMPILE_FLAGS([-Wall -Wextra -pedantic])
+AS_IF(
+    [test "x$ax_enable_debug" = "xyes"],
+    [AX_APPEND_COMPILE_FLAGS([-Werror])]
+)
 
 # Use Address-santizer in debug, if it is available
 AS_IF(

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)