busybox: fix musl build issues

Musl doesn't implemented wmtp, and its utmp support is not sufficient
to build the latest versions of Busybox, so let's disable wtmp and
utmp support in Busybox for musl toolchains.

We re-use an existing define BUSYBOX_INTERNAL_SHADOW_PASSWORDS that
was used to do some musl-related tweaks to the Busybox configuration
around shadow password functions, and extend it to also do the
utmp/wtmp tweaks. In the process, we rename the define to
BUSYBOX_MUSL_TWEAKS.

Note that BUSYBOX_KCONFIG_FIXUP_CMDS continues to call
BUSYBOX_INTERNAL_SHADOW_PASSWORDS because there is another definition
of this macro under other conditions.

Fixes:

  http://autobuild.buildroot.org/results/b96/b96ffad13bca5e6fbf7ce79538aacbfe27b1eff3/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/busybox/busybox.mk

@@ -132,12 +132,18 @@ define BUSYBOX_INTERNAL_SHADOW_PASSWORDS
 endef
 endif
 
-# We also need to use internal functions when using the musl C
-# library, since some of them are not yet implemented by musl.
+# We also need to use internal shadow password functions when using
+# the musl C library, since some of them are not yet implemented by
+# musl.
+#
+# Do not use utmp/wmtp support. wmtp support is not available in musl,
+# and utmp support is not sufficient for Busybox.
 ifeq ($(BR2_TOOLCHAIN_USES_MUSL),y)
-define BUSYBOX_INTERNAL_SHADOW_PASSWORDS
+define BUSYBOX_MUSL_TWEAKS
 	$(call KCONFIG_ENABLE_OPT,CONFIG_USE_BB_PWD_GRP,$(BUSYBOX_BUILD_CONFIG))
 	$(call KCONFIG_ENABLE_OPT,CONFIG_USE_BB_SHADOW,$(BUSYBOX_BUILD_CONFIG))
+	$(call KCONFIG_DISABLE_OPT,CONFIG_FEATURE_UTMP,$(BUSYBOX_BUILD_CONFIG))
+	$(call KCONFIG_DISABLE_OPT,CONFIG_FEATURE_WTMP,$(BUSYBOX_BUILD_CONFIG))
 endef
 endif
 
@@ -223,6 +229,7 @@ define BUSYBOX_KCONFIG_FIXUP_CMDS
 	$(BUSYBOX_SET_INIT)
 	$(BUSYBOX_SET_WATCHDOG)
 	$(BUSYBOX_SET_SELINUX)
+	$(BUSYBOX_MUSL_TWEAKS)
 endef
 
 define BUSYBOX_CONFIGURE_CMDS