build: use a include directory and not relative paths

in older meson versions relative paths are sometimes evalulated from the
build directory and sometimes from the source diretory.

src/bin/meson.build

@@ -21,6 +21,8 @@ src = files([
   'edi_searchpanel.h',
 ])
 
+bin_dir = include_directories('.')
+
 foreach package : packages
    subdir(package)
 endforeach

src/lib/meson.build

@@ -23,6 +23,8 @@ src = files([
   'md5.h',
 ])
 
+lib_dir = include_directories('.')
+
 edi_lib_lib = shared_library('edi', src,
   dependencies : [elm],
   include_directories : top_inc,

src/tests/meson.build

@@ -12,7 +12,7 @@ src = files([
 check = dependency('check')
 
 deps = [elm, check, edi_lib, intl]
-incls = [include_directories('../../../src/bin'), include_directories('../../../src/lib'), top_inc]
+incls = [lib_dir, bin_dir, top_inc]
 
 if get_option('libclang') == true
    deps += [clang]