Suppress armcc warnings about unknown attributes

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@21950 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -2742,6 +2742,7 @@ elif enabled clang; then
 elif enabled armcc; then
     # 2523: use of inline assembler is deprecated
     add_cflags -Wrvct,--diag_suppress=2523
+    add_cflags -Wrvct,--diag_suppress=1207
 elif enabled tms470; then
     add_cflags -pds=824 -pds=837
 fi