package/libpng: fix arm build with NEON

Fixes:
http://autobuild.buildroot.net/results/52c/52c974e70f922e9d7efea4c538e4438a22faa846/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Co-authored-by: Peter Korsgaard <peter@korsgaard.com>
[https://lists.buildroot.org/pipermail/buildroot/2024-November/767661.html]
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libpng/libpng.mk

@@ -16,10 +16,12 @@ LIBPNG_DEPENDENCIES = host-pkgconf zlib
 HOST_LIBPNG_DEPENDENCIES = host-pkgconf host-zlib
 LIBPNG_CONFIG_SCRIPTS = libpng$(LIBPNG_SERIES)-config libpng-config
 LIBPNG_CONF_OPTS = --disable-tools
+LIBPNG_CFLAGS = $(TARGET_CFLAGS)
 
 ifeq ($(BR2_aarch64),y)
 LIBPNG_CONF_OPTS += --enable-arm-neon
 else ifeq ($(BR2_ARM_CPU_HAS_NEON):$(BR2_ARM_SOFT_FLOAT),y:)
+LIBPNG_CFLAGS += -mfpu=neon
 LIBPNG_CONF_OPTS += --enable-arm-neon
 else
 LIBPNG_CONF_OPTS += --disable-arm-neon
@@ -31,5 +33,8 @@ else
 LIBPNG_CONF_OPTS += --disable-intel-sse
 endif
 
+LIBPNG_CONF_ENV = \
+	CFLAGS="$(LIBPNG_CFLAGS)"
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))