Compile only changed files when doing 'make'?

I'm working on a Renesas supplied port of U-Boot, and it seems that 'make' always compiles every single (configured) source file instead compiling only the source files that have been changed since the previous 'make'. I've never run into this before on projects that use 'make', and it makes development of U-Boot rather grueling.

Is that due to something Renesas broke?

Or is that a "feature" of the standard U-Boot Makefile?

-- Grant