[SQUASH ME] Fix some error + simplify some calls

Makefile.buildtests

@@ -206,10 +206,10 @@ info-build:
 	@echo ''
 	@echo -e 'MAKEFILE_LIST:$(patsubst %, \n\t%, $(abspath $(MAKEFILE_LIST)))'
 
-info-boards-supported: BOARDS=$(shell find $(RIOTBASE)/boards/* -maxdepth 0 -type d \! -name *-common)
+info-boards-supported: BOARDS=$(shell find $(RIOTBOARD)/* -maxdepth 0 -type d \! -name *-common -printf '%f ')
 info-boards-supported:
 ifneq (,$(BOARD_WHITELIST))
-	@echo "$(filter $(BOARD_WHITELIST), $(foreach _board, $(BOARDS), $(shell echo "$(_board)" | xargs basename)))"
+	@echo "$(filter $(BOARD_WHITELIST), $(BOARDS))"
 else
-	@echo "$(filter-out $(BOARD_INSUFFICIENT_RAM), $(filter-out $(BOARD_BLACKLIST), $(foreach _board, $(BOARDS), $(shell echo "$(_board)" | xargs basename))))"
+	@echo "$(filter-out $(BOARD_INSUFFICIENT_RAM) $(BOARD_BLACKLIST), $(BOARDS))"
 endif