build-sys: add stub makefiles to make emacs easier to use

diff --git a/src/core/Makefile b/src/core/Makefile
new file mode 120000 (symlink)
index 0000000..d0b0e8e
--- /dev/null
+++ b/src/core/Makefile
@@ -0,0 +1 @@
+../Makefile
\ No newline at end of file

diff --git a/src/shared/Makefile b/src/shared/Makefile
new file mode 120000 (symlink)
index 0000000..d0b0e8e
--- /dev/null
+++ b/src/shared/Makefile
@@ -0,0 +1 @@
+../Makefile
\ No newline at end of file