Refactoring build system for more control of inputs

scripts/templates/exe.boot.j2

@@ -0,0 +1,29 @@
+{% extends "exe.default.j2" %}
+{% block variables %}
+{{ super() }}
+
+ld = ld
+cc = clang
+cxx = clang++
+
+ccflags = $ccflags $
+    -DKERNEL_FILENAME=L\"popcorn.elf\" $
+    -DGNU_EFI_USE_MS_ABI $
+    -DHAVE_USE_MS_ABI $
+    -DEFI_DEBUG=0 $
+    -DEFI_DEBUG_CLEAR_MEMORY=0 $
+	-DBOOTLOADER_DEBUG $
+    -fPIC
+
+ldflags = $ldflags $
+    -T ${srcroot}/src/arch/x86_64/boot.ld $
+    -shared
+
+{% endblock %}
+
+{% block extra %}
+
+build $builddir/boot.efi : makeefi ${builddir}/{{ module.output }}
+    name = boot.efi
+
+{% endblock %}