Fix meson issues for OSX

scripts/clang_build_include_dir.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+if [[ -d /usr/local/opt/llvm ]]; then
+  echo "/usr/local/opt/llvm/include"
+fi
+

src/bin/meson.build

@@ -26,13 +26,19 @@ foreach package : packages
 endforeach
 
 deps = [elm, edi_lib, intl]
+incls = []
 
 if get_option('libclang') == true
    deps += [clang]
+
+   clang_build_include_dir_command = run_command(find_program('../../scripts/clang_build_include_dir.sh'))
+   clang_build_include_dir = clang_include_dir_command.stdout().strip()
+   incls += include_directories(clang_build_include_dir)
 endif
 
 executable('edi', src,
   dependencies : deps,
+  include_directories : incls,
   install : true
 )