libselinux: fix compilation with musl 1.2.4

musl 1.2.4 deprecated legacy "LFS64" ("large file support") interfaces so
just having _GNU_SOURCE defined is not enough anymore.

_LARGEFILE64_SOURCE has to be defined in the source, or CFLAGS can be used
to pass -D_LARGEFILE64_SOURCE to allow to keep using LFS64 definitions.

Signed-off-by: Robert Marko <[email protected]>

package/libs/libselinux/Makefile

@@ -115,6 +115,7 @@ HOST_MAKE_FLAGS += \
 
 ifeq ($(CONFIG_USE_MUSL),y)
 MAKE_FLAGS += FTS_LDLIBS=-lfts
+TARGET_CFLAGS += -D_LARGEFILE64_SOURCE
 endif
 
 MAKE_FLAGS += \