configure: initialise all flag filters at the same place

This is more consistent, and doing it earlier is harmless.
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -1708,6 +1708,8 @@ LIB_INSTALL_EXTRA_CMD='$$(RANLIB) "$(LIBDIR)/$(LIBNAME)"'
 SLIB_INSTALL_NAME='$(SLIBNAME_WITH_VERSION)'
 SLIB_INSTALL_LINKS='$(SLIBNAME_WITH_MAJOR) $(SLIBNAME)'
 
+asflags_filter=echo
+cflags_filter=echo
 ldflags_filter=echo
 
 AS_O='-o $@'
@@ -1949,9 +1951,6 @@ EOF
     die "Sanity test failed."
 fi
 
-asflags_filter=echo
-cflags_filter=echo
-
 if   $cc -v 2>&1 | grep -q '^gcc.*LLVM'; then
     cc_type=llvm_gcc
     gcc_extra_ver=$(expr "$($cc --version | head -n1)" : '.*\((.*)\)')