Check for may_alias gcc attribute support

Originally committed as revision 21522 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -985,6 +985,7 @@ HAVE_LIST="
     alsa_asoundlib_h
     altivec_h
     arpa_inet_h
+    attribute_may_alias
     attribute_packed
     bswap
     closesocket
@@ -2298,6 +2299,10 @@ check_cc <<EOF && enable attribute_packed
 struct { int x; } __attribute__((packed)) x;
 EOF
 
+check_cc <<EOF && enable attribute_may_alias
+union { int x; } __attribute__((may_alias)) x;
+EOF
+
 check_cc <<EOF || die "endian test failed"
 unsigned int endian = 'B' << 24 | 'I' << 16 | 'G' << 8 | 'E';
 EOF