json-c: Backport --disable-werror patch to allow compilation under icecc

icecc preprocesses source files locally before shipping them off to be compiled
on remote hosts. This preprocessing removes comments, including /* fallthough */
comments in switch statements that normally prevent an implicit-fallthrough
warning, see https://github.com/icecc/icecream/issues/419

Rather than turning off -Werror, the upstream project has implemented a
configure option, --disable-werror, in response to Ross's
https://github.com/json-c/json-c/issues/489

This patch from
https://github.com/json-c/json-c/commit/21c886534f8927fdc0fb5f8647394f3e0e0874b8

Upstream-Status: Backport [Not yet released]
Signed-off-by: Douglas Royds <douglas.royds@taitradio.com>

From 21c886534f8927fdc0fb5f8647394f3e0e0874b8 Mon Sep 17 00:00:00 2001
From: Pierce Lopez <pierce.lopez@gmail.com>
Date: Sun, 9 Jun 2019 10:52:08 -0400
Subject: [PATCH] build: add --disable-werror option to configure

to omit -Werror compiler option
---
 configure.ac | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 272ea6af9c..798fd5b747 100644
--- a/configure.ac
+++ b/configure.ac
@@ -165,7 +165,12 @@ AS_IF([test "x$enable_Bsymbolic" = "xcheck"],
 AS_IF([test "x$enable_Bsymbolic" = "xyes"], [JSON_BSYMBOLIC_LDFLAGS=-Wl[,]-Bsymbolic-functions])
 AC_SUBST(JSON_BSYMBOLIC_LDFLAGS)
 
-AX_APPEND_COMPILE_FLAGS([-Wall -Werror -Wcast-qual -Wno-error=deprecated-declarations])
+AC_ARG_ENABLE([werror],
+    AS_HELP_STRING([--disable-werror], [avoid treating compiler warnings as fatal errors]))
+
+AS_IF([test "x$enable_werror" != "xno"], [AX_APPEND_COMPILE_FLAGS([-Werror])])
+
+AX_APPEND_COMPILE_FLAGS([-Wall -Wcast-qual -Wno-error=deprecated-declarations])
 AX_APPEND_COMPILE_FLAGS([-Wextra -Wwrite-string -Wno-unused-parameter])
 AX_APPEND_COMPILE_FLAGS([-D_GNU_SOURCE])