build: simplify include_directories

Define common_inc which includes both public_inc and the project root directory.
The project root directory will allow access to config.h and all the shared/
headers.

Replacing all custom '.', '..', '../..', '../shared' etc. include paths with
common_inc reduces clutter in the target definitions and enforces the common
 #include directive style, as e.g. including shared/ headers without the
subdirectory name no longer works.

Unfortunately this does not prevent one from using private libweston headers
with the usual include pattern for public headers.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

ivi-shell/meson.build

@@ -11,7 +11,7 @@ if get_option('shell-ivi')
 	plugin_shell_ivi = shared_library(
 		'ivi-shell',
 		srcs_shell_ivi,
-		include_directories: include_directories('..', '../shared'),
+		include_directories: common_inc,
 		dependencies: [ dep_lib_desktop, dep_libweston ],
 		name_prefix: '',
 		install: true,
@@ -29,7 +29,7 @@ if get_option('shell-ivi')
 	plugin_ivi_hmi = shared_library(
 		'hmi-controller',
 		srcs_ivi_hmi,
-		include_directories: include_directories('..', '../shared'),
+		include_directories: common_inc,
 		dependencies: [ dep_libweston, dep_libshared ],
 		name_prefix: '',
 		install: true,