Trace every subprocess created

I have a project with fairly large makefiles, and they tend to grow slower over time (even when nothing needs to be done).

Most of this slowdown is because there are many variables instantiated by executing subprocess:

ANSWER=$(shell echo 1 + 41 | bc)

The fix is typically easy (find another way to do it, or at least assign using :=), but the problem is finding all these (and measuring the impact of each, since 100 echos can be much faster than a single bc)

Unfortunately neither make nor remake seem to provide a way to trace this.

$ cat Makefile
ANSWER=$(shell echo 1 + 41 | bc)
all:
	@echo ANSWER=$(ANSWER)%

$ make --debug=all | grep bc
[no output]

$ remake --trace=full | grep bc
[no output]

So it would be nice if remake provided a way to trace every subprocess created by make (and maybe even how long it took to execute).

Reproduce the Makefile example and compare make --debug=all with remake --trace=full, confirming that the bc subprocess is not reported. Then inspect the existing tracing entry points and define how every subprocess should be emitted, with execution time included if supported; done means the example's subprocess is traceable.