package/v4l2loopback: fix v4l2loopback-ctl compile/install

Since upstream commit [1] the original v4l2loopback-ctl bash script was
replaced by a C version, so add a proper compile step (and remove bash
runtime dependency) to fix '[help] v4l2loopback package build fails for
raspberrypi5' [2].

The issue can be reproduced with the commands:

    cat <<EOF >.config
    BR2_aarch64=y
    BR2_TOOLCHAIN_EXTERNAL=y
    BR2_LINUX_KERNEL=y
    BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
    BR2_PACKAGE_V4L2LOOPBACK=y
    BR2_PACKAGE_V4L2LOOPBACK_UTILS=y
    EOF
    make olddefconfig
    make v4l2loopback

Note: upstream commit [1] was introduced in version v0.13.0.
Buildroot bumped v4l2loopback to v0.13.2 in [3].

Fixes:

  /usr/bin/install: cannot stat
  '.../build/v4l2loopback-0.13.2/utils/v4l2loopback-ctl':
  No such file or directory

[1] https://github.com/v4l2loopback/v4l2loopback/commit/33922fa4e9965d400edcc2761e55fedf84bbb22a
[2] https://lists.busybox.net/pipermail/buildroot/2025-March/775911.html
[3] https://gitlab.com/buildroot.org/buildroot/-/commit/02540771bccf7b10c7daecce5f0e1e41a73c1e07

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
[Julien:
 - add commands to reproduce the issue
 - add reference to buildroot commit introducing the issue
]
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 5d85d23e16fdf9e6574e2a3cbdf4d27d17cd6942)
Signed-off-by: Thomas Perale <thomas.perale@mind.be>

package/v4l2loopback/Config.in

@@ -14,10 +14,6 @@ if BR2_PACKAGE_V4L2LOOPBACK
 
 config BR2_PACKAGE_V4L2LOOPBACK_UTILS
 	bool "utils"
-	depends on BR2_USE_MMU # bash
-	select BR2_PACKAGE_BUSYBOX_SHOW_OTHERS # bash
-	select BR2_PACKAGE_BASH # runtime dependency
-	select BR2_PACKAGE_SUDO # runtime dependency
 	help
 	  Install applications to interact with v4l2-loopback devices
 	  ("virtual video devices").  Currently there is only a single

package/v4l2loopback/v4l2loopback.mk

@@ -11,6 +11,10 @@ V4L2LOOPBACK_LICENSE_FILES = COPYING
 V4L2LOOPBACK_CPE_ID_PREFIX = cpe:2.3:o
 
 ifeq ($(BR2_PACKAGE_V4L2LOOPBACK_UTILS),y)
+define V4L2LOOPBACK_BUILD_CMDS
+	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) -C $(@D) utils
+endef
+
 define V4L2LOOPBACK_INSTALL_TARGET_CMDS
 	$(INSTALL) -D -m 0755 $(@D)/utils/v4l2loopback-ctl $(TARGET_DIR)/usr/bin/v4l2loopback-ctl
 endef