Quoting problems (or: why doesn't my new configure script work?)

[ness]

My new idl4 interface and features seem to work. Now I wanted to change
the configure.ac to find idl4, set IDL4FLAGS and test whether idl4 is
new enough. One of my changes requires that one gives the compiler call
to idl4, as ONE parameter. My try looks like that:
(CFLAGS, CC and IDL4 are legal)

IDL4FLAGS="$IDL4FLAGS -i V4_GNU -p generic -T -C \"$CC $CFLAGS\""
echo -n "checking for idl4 -l -i V4_GNU... "
$IDL4 $IDL4FLAGS -l -c test.idl
if test -e test_client.h;then
echo yes
rm test_client.h
else
echo 'Your version of idl4 is outdated, see README.idl4!'
exit 1
fi

But it doesn't work. It looks like idl4 doesn't get the compiler call
quoted.
Cleartext: The line $IDL4 $IDL4FLAGS -l -c test.idl should be expanded
to e.g. idl4 -i V4_GNU -p generic -T -C "gcc -O3 -std=gnu99" -c test.idl
but gets expanded to idl4 -i V4_GNU -p generic -T -C gcc -O3
-std=gnu99 -c test.idl. Why?
I only ask here since I got no answer elsewhere