test: Add an external-check target

To go along with core-check and friends.

Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Vasant Hegde <hegdevasant@linux.vnet.ibm.com>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

Author: oohal

external/Makefile.check

@@ -6,9 +6,11 @@ CHECK_TOOL=$(patsubst %,check-%,$(TOOL))
 TOOL_COVERAGE=$(patsubst %,%-coverage,$(TOOL))
 TOOL_TEST_CLEAN=$(patsubst %,%-test-clean,$(TOOL))
 
+.PHONY: external-check
+external-check: $(CHECK_TOOL)
 
 .PHONY: check
-check: $(CHECK_TOOL)
+check: external-check
 
 #Makefile knows to build and clean it before checking, should also
 #make clean before checking. If not, .o files for different