meson: Fix wrapper handling of implicit setup command

meson: Fix wrapper handling of implicit setup command

From an SDK, running a meson setup build without an explicit setup
command can result in a native build when a cross build is expected.

The problem is in meson-wrapper where it tries to detect whether a
setup command is being used. The logic looks through all arguments for
a command, and the first argument it finds that doesn't start with a -
is treated as the command. This doesn't work for an implicit setup
command if any option with a space-separated argument exists. In this
case, the argument is incorrectly selected as the command, causing the
setup command options for the cross build to be excluded from the
command line, and thus a native build.

Improve the logic by just looking at the first argument. If it is
a known comand, then record it. Otherwise just assume it is the
implicit setup command.

Note that this fix does not address the possibility of a new meson
command. Two new echo statements are included to help the user in case
of trouble:

```
~/git/weston-imx$ meson --warnlevel 3 --prefix=/usr -Ddoc=false -Dbackend-drm-screencast-vaapi=false -Dcolor-management-lcms=false -Dpipewire=false -Dbackend-x11=false -Dxwayland=true -Dsimple-clients=all -Dbackend-wayland=false  -Dbackend-default=drm -Dbackend-rdp=false -Dtest-junit-xml=false -Dlauncher-libseat=false -Dimage-jpeg=false -Dimage-webp=false -Drenderer-g2d=true build
meson-wrapper: Implicit setup command assumed
meson-wrapper: Running meson with setup options: " --cross-file=/opt/fsl-imx-internal-xwayland/6.1-langdale/sysroots/x86_64-pokysdk-linux/usr/share/meson/aarch64-poky-linux-meson.cross --native-file=/opt/fsl-imx-internal-xwayland/6.1-langdale/sysroots/x86_64-pokysdk-linux/usr/share/meson/meson.native "
The Meson build system
Version: 0.63.3
```

Signed-off-by: Tom Hochstein <tom.hochstein@nxp.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>