Add a linuxlike test case for subdir include order

Needs glib-2.0 as a pkg-config dependency

test cases/linuxlike/6 subdir include order/meson.build

@@ -0,0 +1,12 @@
+project('subdir include order', 'c')
+
+# Ensure that headers in subdirs override external dependencies
+cc = meson.get_compiler('c')
+
+glib = dependency('glib-2.0')
+
+# This will fail to compile if it picks up the system-installed glib instead of
+# the glib in the subdir
+executable('prog', 'prog.c',
+  include_directories : include_directories('subdir'),
+  dependencies : glib)

test cases/linuxlike/6 subdir include order/prog.c

@@ -0,0 +1,7 @@
+#include <glib.h>
+
+#ifndef MESON_OUR_GLIB
+#error "Failed"
+#endif
+
+int main() { return 0; }

test cases/linuxlike/6 subdir include order/subdir/glib.h

@@ -0,0 +1 @@
+#define MESON_OUR_GLIB 1