Revamp all the Makefiles (thanks @fincs @WinterMute)

... dependencies are now properly handled (e.g. header changes, etc.)

fusee/fusee-primary/linker.specs

@@ -1,7 +1,7 @@
 %rename link                old_link
 
 *link:
-%(old_link) -T linker.ld --nmagic --gc-sections
+%(old_link) -T %:getenv(TOPDIR /linker.ld) --nmagic --gc-sections
 
 *startfile:
 crti%O%s crtbegin%O%s