mpv: Link libatomic on riscv64

gcc uses __atomic_compare_exchange_1 which is not implemented for rv64

Fixes
video/out/vo_libmpv.c:186: undefined reference to `__atomic_compare_exchange_1'
collect2: error: ld returned 1 exit status

Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-oe/recipes-multimedia/mplayer/mpv_0.32.0.bb

@@ -26,6 +26,8 @@ S = "${WORKDIR}/git"
 
 inherit waf pkgconfig mime-xdg
 
+LDFLAGS_append_riscv64 = " -latomic"
+
 LUA ?= "lua"
 LUA_mips64  = ""
 LUA_aarch64  = ""