package/rpi-rgb-led-matrix: needs -fPIC

Fix the following build failure raised since the addition of the package
in commit e821078031e14df69e5142f23e9cb7b5a1ea0e77:

/home/buildroot/autobuild/instance-2/output-1/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-buildroot-linux-gnu/9.3.0/../../../../aarch64-buildroot-linux-gnu/bin/ld: led-matrix.o: relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `_ZTVN10rgb_matrix11FrameCanvasE' which may bind externally can not be used when making a shared object; recompile with -fPIC

Fixes:
 - http://autobuild.buildroot.org/results/be291d6b0efdc1914babfb4a9be5eb863058eaf5

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/rpi-rgb-led-matrix/rpi-rgb-led-matrix.mk

@@ -10,8 +10,12 @@ RPI_RGB_LED_MATRIX_LICENSE = GPL-2.0
 RPI_RGB_LED_MATRIX_LICENSE_FILES = COPYING
 RPI_RGB_LED_MATRIX_INSTALL_STAGING = YES
 
+RPI_RGB_LED_MATRIX_MAKE_OPTS = \
+	$(TARGET_CONFIGURE_OPTS) \
+	CXXFLAGS="$(TARGET_CXXFLAGS) -fPIC"
+
 define RPI_RGB_LED_MATRIX_BUILD_CMDS
-	$(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D)/lib all
+	$(MAKE) $(RPI_RGB_LED_MATRIX_MAKE_OPTS) -C $(@D)/lib all
 endef
 
 define RPI_RGB_LED_MATRIX_INSTALL_STAGING_CMDS
@@ -31,7 +35,7 @@ ifeq ($(BR2_PACKAGE_RPI_RGB_LED_MATRIX_IMAGE_VIEWER),y)
 RPI_RGB_LED_MATRIX_DEPENDENCIES += graphicsmagick
 
 define RPI_RGB_LED_MATRIX_BUILD_IMAGE_VIEWER_CMDS
-	$(MAKE) $(TARGET_CONFIGURE_OPTS) \
+	$(MAKE) $(RPI_RGB_LED_MATRIX_MAKE_OPTS) \
 		MAGICK_CXXFLAGS="-I$(STAGING_DIR)/usr/include/GraphicsMagick $(shell $(STAGING_DIR)/usr/bin/GraphicsMagick++-config --cxxflags)" \
 		MAGICK_LDFLAGS="-L$(STAGING_DIR)/usr/lib $(shell $(STAGING_DIR)/usr/bin/GraphicsMagick++-config --libs)" \
 		-C $(@D)/utils led-image-viewer
@@ -46,7 +50,7 @@ endif
 
 ifeq ($(BR2_PACKAGE_RPI_RGB_LED_MATRIX_TEXT_SCROLLER),y)
 define RPI_RGB_LED_MATRIX_BUILD_TEXT_SCROLLER_CMDS
-	$(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D)/utils text-scroller
+	$(MAKE) $(RPI_RGB_LED_MATRIX_MAKE_OPTS) -C $(@D)/utils text-scroller
 endef
 RPI_RGB_LED_MATRIX_POST_BUILD_HOOKS += RPI_RGB_LED_MATRIX_BUILD_TEXT_SCROLLER_CMDS
 
@@ -62,7 +66,7 @@ ifeq ($(BR2_PACKAGE_RPI_RGB_LED_MATRIX_VIDEO_VIEWER),y)
 RPI_RGB_LED_MATRIX_DEPENDENCIES += ffmpeg
 
 define RPI_RGB_LED_MATRIX_BUILD_VIDEO_VIEWER_CMDS
-	$(MAKE) $(TARGET_CONFIGURE_OPTS) \
+	$(MAKE) $(RPI_RGB_LED_MATRIX_MAKE_OPTS) \
 		AV_CXXFLAGS="$(shell $(HOST_DIR)/bin/pkg-config --cflags libavcodec libavformat libswscale libavutil)" \
 		AV_LDFLAGS="$(shell $(HOST_DIR)/bin/pkg-config --libs libavcodec libavformat libswscale libavutil)" \
 		-C $(@D)/utils video-viewer