build: fix race with creating qapi-generated

Since qapi-generated/ is a global QEMU include path, we need to make
sure it is created before anything is compiled, so do this in the
configure phase rather than via the Makefile.
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -3622,7 +3622,7 @@ DIRS="tests tests/cris slirp audio block net pc-bios/optionrom"
 DIRS="$DIRS pc-bios/spapr-rtas"
 DIRS="$DIRS roms/seabios roms/vgabios"
 DIRS="$DIRS fsdev ui"
-DIRS="$DIRS qapi"
+DIRS="$DIRS qapi qapi-generated"
 DIRS="$DIRS qga trace"
 FILES="Makefile tests/Makefile qdict-test-data.txt"
 FILES="$FILES tests/cris/Makefile tests/cris/.gdbinit"