lib: add reasons for components being disabled

For each library where we optionally disable it, add in the reason why it's
being disabled, so the user knows how to fix it.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Luca Boccassi <bluca@debian.org>

lib/librte_kni/meson.build

@@ -3,6 +3,7 @@
 
 if not is_linux or not dpdk_conf.get('RTE_ARCH_64')
 	build = false
+	reason = 'only supported on 64-bit linux'
 endif
 version = 2
 sources = files('rte_kni.c')

lib/librte_power/meson.build

@@ -3,6 +3,7 @@
 
 if not is_linux
 	build = false
+	reason = 'only supported on linux'
 endif
 sources = files('rte_power.c', 'power_acpi_cpufreq.c',
 		'power_kvm_vm.c', 'guest_channel.c',

lib/librte_telemetry/meson.build

@@ -12,4 +12,5 @@ if jansson.found()
 	dpdk_app_link_libraries += ['telemetry']
 else
 	build = false
+	reason = 'missing dependency "jansson"'
 endif

lib/librte_vhost/meson.build

@@ -3,6 +3,7 @@
 
 if not is_linux
 	build = false
+	reason = 'only supported on linux'
 endif
 if has_libnuma == 1
 	dpdk_conf.set10('RTE_LIBRTE_VHOST_NUMA', true)