Building plugin sources doesn't produce any output to 'make'

Generally, if you run 'make' and it recompiles a source file, it tells you so. For instance touching the source file system/main.c results in recompilation of some .o files, which we get told about:

$ touch system/main.c 
$ make -C build/arm-clang/
make: Entering directory '/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang'
[1/26] Generating subprojects/dtc/version_gen.h with a custom command
[2/26] Generating qemu-version.h with a custom command (wrapped by meson to capture output)
[3/6] Compiling C object qemu-system-arm.p/system_main.c.o
[4/6] Linking target qemu-system-arm
[5/6] Compiling C object qemu-system-aarch64.p/system_main.c.o
[6/6] Linking target qemu-system-aarch64
make: Leaving directory '/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang'

However, if you do the same for the source of a plugin in contrib/plugins this doesn't work:

$ ls -l build/arm-clang/contrib/plugins/cache.o 
-rw-r--r-- 1 petmay01 petmay01 151872 Jul 25 17:58 build/arm-clang/contrib/plugins/cache.o
$ touch contrib/plugins/cache.c
$ make -C build/arm-clang/
make: Entering directory '/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang'
[1/24] Generating subprojects/dtc/version_gen.h with a custom command
[2/24] Generating qemu-version.h with a custom command (wrapped by meson to capture output)
make: Leaving directory '/mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/arm-clang'
$ ls -l build/arm-clang/contrib/plugins/cache.o 
-rw-r--r-- 1 petmay01 petmay01 151872 Jul 25 18:06 build/arm-clang/contrib/plugins/cache.o

We can see by looking at the timestamps on the cache.o file that the build system correctly determined that it needed to recompile cache.o. However there is no output, so it looks to the user as if it did nothing, resulting in perhaps the mistaken belief that this build config isn't building plugins at all.

Plugin compilation should produce the same kind of progress output as when building anything else.