build: avoid C99 for loop

build: avoid C99 for loop

Although we require various C99 features, we don't yet require a
complete C99 compiler.  On RHEL 5, compilation complained:

qemu/qemu_command.c: In function 'qemuBuildGraphicsCommandLine':
qemu/qemu_command.c:4688: error: 'for' loop initial declaration used outside C99 mode

* src/qemu/qemu_command.c (qemuBuildGraphicsCommandLine): Declare
variable sooner.
* src/qemu/qemu_process.c (qemuProcessInitPasswords): Likewise.