build: Add meson support

Add support for buildling with meson.

Support for --enable-oe-sdk is dropped because running unit tests on the
build system is now supported directly with meson subprojects:

meson buildir && ninja -C buildir test

I tested this by building a witherspoon image and booting it to
multi-user and verifying the mapper-wait functionality works correctly.

Change-Id: I86e5efc7b7c89183219a4c890ad658e334765fc1
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/.gitignore b/.gitignore
index 6b2bed0..cbe1832 100644
--- a/.gitignore
+++ b/.gitignore
@@ -119,3 +119,6 @@
 src/test/need_to_introspect
 src/test/well_known
 src/test/name_change
+build*/
+subprojects/*
+!subprojects/*.wrap