gcc fails if we compile with -O3

libavcodec/sbrdsp.c: In function 'sbr_neg_odd_64_c':
libavcodec/sbrdsp.c:47:13: internal compiler error: in vect_analyze_data_ref_accesses, at tree-vect-data-refs.c:2596
 static void sbr_neg_odd_64_c(float *x)
             ^

We work around it by using -O2 which is more sane.

http://bugs.alpinelinux.org/issues/5334

diff --git a/configure b/configure
index 5e788ac..aa34f9b 100755
--- a/configure
+++ b/configure
@@ -3795,7 +3795,7 @@ probe_cc(){
                 warn "gcc 4.2 is outdated and may miscompile FFmpeg. Please use a newer compiler." ;;
             esac
         fi
-        _cflags_speed='-O3'
+        _cflags_speed='-O2'
         _cflags_size='-Os'
     elif $_cc --version 2>/dev/null | grep -q ^icc; then
         _type=icc