package/irrlicht: disable bundled libpng NEON support

Irrlicht fail to detect properly the NEON support on aarch64 or ARM with NEON FPU support.
While linking an application with libIrrlicht.so, we get an undefined reference to
png_init_filter_functions_neon.
Some files are missing in the libpng bundled in Irrlicht, in particular arm/arm_init.c [1],
so disable NEON support completely.

This can be reproduced by building minetest using this defconfig for aarch64:
BR2_aarch64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_PACKAGE_MINETEST=y
BR2_PACKAGE_MINETEST_CLIENT=y
BR2_PACKAGE_MINETEST_SERVER=y
BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_GALLIUM_DRIVER_SWRAST=y
BR2_PACKAGE_MESA3D_OPENGL_GLX=y
BR2_PACKAGE_XORG7=y

Or for ARM with NEON FPU support:
BR2_arm=y
BR2_cortex_a15=y
BR2_ARM_FPU_NEON=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_PACKAGE_MINETEST=y
BR2_PACKAGE_MINETEST_CLIENT=y
BR2_PACKAGE_MINETEST_SERVER=y
BR2_PACKAGE_MESA3D=y
BR2_PACKAGE_MESA3D_GALLIUM_DRIVER_SWRAST=y
BR2_PACKAGE_MESA3D_OPENGL_GLX=y
BR2_PACKAGE_XORG7=y

[1] https://github.com/glennrp/libpng/tree/v1.6.37/arm

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit bf5f4f417a9e6e7eed5ea6a99c26583958890515)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/irrlicht/irrlicht.mk

@@ -38,6 +38,13 @@ ifeq ($(BR2_STATIC_LIBS),)
 IRRLICHT_CONF_OPTS += sharedlib
 endif
 
+# Irrlicht fail to detect properly the NEON support on aarch64 or ARM with NEON FPU support.
+# While linking an application with libIrrlicht.so, we get an undefined reference to
+# png_init_filter_functions_neon.
+# Some files are missing in the libpng bundled in Irrlicht, in particular arm/arm_init.c,
+# so disable NEON support completely.
+IRRLICHT_CONF_OPTS += CPPFLAGS="$(TARGET_CPPFLAGS) -DPNG_ARM_NEON_OPT=0"
+
 define IRRLICHT_BUILD_CMDS
 	$(TARGET_MAKE_ENV)
 		$(MAKE) -C $(@D)/$(IRRLICHT_SUBDIR) $(IRRLICHT_CONF_OPTS)