When building SWUpdate with the following defconfig:
```
CONFIG_DOWNLOAD=y
```
.. the build process breaks with:
```
corelib/channel_curl.c:27:10: fatal error: json-c/json.h: No such file or directory
#include <json-c/json.h>
```
Looking at the SWUpdate Kconfig based build system shows that `CONFIG_DOWNLOAD`
depends on `HAVE_LIBCURL`, which selects CURL, which eventually enables the
(unnecessary) build of channel_curl.o.
The upstream fixes the condition for building channel_curl.o by adding a new
hidden config option `CHANNEL_CURL`, which is only selected by the
dependent options.
Backported from:
37a6666a53
Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
f8fcece3a1