armcc: filter out non-gcc options from ASFLAGS

This allows passing armcc-specific flags with --extra-cflags without
choking the assembler.
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -1912,6 +1912,7 @@ elif $cc --vsn 2>/dev/null | grep -q "ARM C/C++ Compiler"; then
     AS_DEPFLAGS='-MMD'
     speed_cflags='-O3'
     size_cflags='-Os'
+    filter_asflags="filter_out -W${armcc_opt}*"
 elif $cc -version 2>/dev/null | grep -q TMS470; then
     cc_type=tms470
     cc_version="AV_STRINGIFY(__TI_COMPILER_VERSION__)"