Also test make clean in library

Don't test `make clean` at the toplevel, that would be too much work (we'd
need to support `$(RM)` in all makefiles, and arrange for `find` as well for
`clean_more_on_top`).

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

library/Makefile

@@ -389,10 +389,12 @@ $(GENERATED_WRAPPER_FILES):
 
 psa_crypto.o:psa_crypto_driver_wrappers.h
 
+RM ?= rm
+
 clean:
 ifndef WINDOWS
-	rm -f *.o *.s libmbed*
-	rm -f $(THIRDPARTY_CRYPTO_OBJECTS) $(THIRDPARTY_CRYPTO_OBJECTS:.o=.s)
+	$(RM) -f *.o *.s libmbed*
+	$(RM) -f $(THIRDPARTY_CRYPTO_OBJECTS) $(THIRDPARTY_CRYPTO_OBJECTS:.o=.s)
 else
 	if exist *.o del /Q /F *.o
 	if exist *.s del /Q /F *.s
@@ -402,7 +404,7 @@ endif
 
 neat: clean
 ifndef WINDOWS
-	rm -f $(GENERATED_FILES)
+	$(RM) -f $(GENERATED_FILES)
 else
 	for %f in ($(subst /,\,$(GENERATED_FILES))) if exist %f del /Q /F %f
 endif

tests/scripts/components-build-system.sh

@@ -50,6 +50,8 @@ component_build_make_no_gen_files () {
     # GCC needs "as" in $PATH by default. To use GCC, we need to tell it where
     # to find the assembler. Or we can use clang which just works.
     CC="$(command -v clang)"
+    # For cleaning.
+    RM="$(command -v rm)"
 
     # Test the build with make.
     # Preferably we should also test with CMake. Note that a CMake test