monitor: add cli11 argument parsing

Replace our custom argument parser with one from CLIUtils.

This results in a number of minor behavioral differences.
 - The -? option is no longer recognized as an alias for -h/--help.
 - The original parser returned EXIT_FAILURE in all cases, but CLIUtils
   uses different non-zero error codes in different situations.
 - Minor changes to help text descriptions:
----new----
Usage: build/phosphor-unit-failure-monitor.new [OPTIONS]

Options:
  -h,--help                   Print this help message and exit
  -s,--source TEXT REQUIRED
  -t,--target TEXT REQUIRED
  -a,--action ENUM:value in {start->0,stop->1} OR {0,1} REQUIRED

----old----
Usage: build/phosphor-unit-failure-monitor [options]
Options:
    --help             Print this menu
    --source=<source>  The source unit to monitor
    --target=<target>  The target unit to start or stop
    --action=<action>  Target unit action - start or stop

 - The original parser displays the full help text on error, CLIUtils
   does not:

----new----
$ phosphor-unit-failure-monitor
--source is required
Run with --help for more information.

----old----
$ phosphor-unit-failure-monitor
ERROR: Source not specified
Usage: build/phosphor-unit-failure-monitor [options]
Options:
    --help             Print this menu
    --source=<source>  The source unit to monitor
    --target=<target>  The target unit to start or stop
    --action=<action>  Target unit action - start or stop

Change-Id: I2417d9c857c6d8fc04807fe4729d2fa154e746a3
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meson.build b/meson.build
index 209c49f..a7f3a4f 100644
--- a/meson.build
+++ b/meson.build
@@ -12,6 +12,13 @@
     version: '1.0',
 )
 
+cxx = meson.get_compiler('cpp')
+
+if cxx.has_header('CLI/CLI.hpp')
+    cli11_dep = declare_dependency()
+else
+    cli11_dep = dependency('cli11')
+endif
 phosphor_logging = dependency('phosphor-logging')
 phosphor_dbus_interfaces = dependency('phosphor-dbus-interfaces')
 sdbusplus = dependency('sdbusplus')
@@ -104,11 +111,11 @@
 executable(
     'phosphor-unit-failure-monitor',
     [
-        'fail-monitor/argument.cpp',
         'fail-monitor/main.cpp',
         'fail-monitor/monitor.cpp',
     ],
     dependencies: [
+        cli11_dep,
         phosphor_logging,
     ],
     install: true