meson: remove implicit_include_directories

We don't generate any headers so skip looking for them in the build
tree, which results in simpler compiler command lines and a minor
efficiency improvement.  Tested by building and running the unit tests.

Change-Id: Ib666bf2b49922d9e495325948df10f1d06026b56
Signed-off-by: Brad Bishop <bradbish@qti.qualcomm.com>
diff --git a/meson.build b/meson.build
index d170cf3..e7930ee 100644
--- a/meson.build
+++ b/meson.build
@@ -104,6 +104,7 @@
         dependency('threads'),
         dependency('tinyxml2', default_options: ['tests=false']),
     ],
+    implicit_include_directories: false,
     install: true,
     install_dir: join_paths(
         get_option('prefix'),
@@ -160,6 +161,7 @@
         'phosphor-unit-failure-monitor',
         ['fail-monitor/main.cpp', 'fail-monitor/monitor.cpp'],
         dependencies: [cli11, phosphor_logging, sdbusplus],
+        implicit_include_directories: false,
         install: true,
     )
 endif