package/opencv3: use external protobuf instead of bundled one

Since version 3.3.0 and its commit
1c4c58d1b5,
opencv3 bundles its own copy of protobuf. Instead of using the bundled
protobuf library, this commit disables building protobuf
(BUILD_PROTOBUF=OFF) and instead uses the protobuf Buildroot package
(using the WITH_PROTOBUF=ON/OFF option).

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/opencv3/Config.in

@@ -307,6 +307,18 @@ config BR2_PACKAGE_OPENCV3_WITH_PNG
 	help
 	  Use shared libpng from the target system.
 
+config BR2_PACKAGE_OPENCV3_WITH_PROTOBUF
+	bool "protobuf support"
+	depends on BR2_PACKAGE_PROTOBUF_ARCH_SUPPORTS # protobuf
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_8 # protobuf
+	select BR2_PACKAGE_PROTOBUF
+	help
+	  Use shared protobuf from the target system.
+
+comment "protobuf support needs a toolchain w/ gcc >= 4.8"
+	depends on BR2_PACKAGE_PROTOBUF_ARCH_SUPPORTS
+	depends on !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
+
 config BR2_PACKAGE_OPENCV3_WITH_TIFF
 	bool "tiff support"
 	select BR2_PACKAGE_TIFF

package/opencv3/opencv3.mk

@@ -193,6 +193,7 @@ OPENCV3_CONF_OPTS += \
 	-DBUILD_JPEG=OFF \
 	-DBUILD_OPENEXR=OFF \
 	-DBUILD_PNG=OFF \
+	-DBUILD_PROTOBUF=OFF \
 	-DBUILD_TIFF=OFF \
 	-DBUILD_ZLIB=OFF \
 	-DINSTALL_C_EXAMPLES=OFF \
@@ -288,6 +289,13 @@ else
 OPENCV3_CONF_OPTS += -DWITH_PNG=OFF
 endif
 
+ifeq ($(BR2_PACKAGE_OPENCV3_WITH_PROTOBUF),y)
+OPENCV3_CONF_OPTS += -DWITH_PROTOBUF=ON
+OPENCV3_DEPENDENCIES += protobuf
+else
+OPENCV3_CONF_OPTS += -DWITH_PROTOBUF=OFF
+endif
+
 ifeq ($(BR2_PACKAGE_OPENCV3_WITH_QT5),y)
 OPENCV3_CONF_OPTS += -DWITH_QT=5
 OPENCV3_DEPENDENCIES += qt5base