Add target to generated all .c (and .datax) files

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/Makefile b/tests/Makefile
index 6e232c9..44ff43c 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -108,6 +108,7 @@
 	$(CC) $(LOCAL_CFLAGS) $(CFLAGS) -o $@ -c $<
 
 C_FILES := $(addsuffix .c,$(APPS))
+c: $(C_FILES)
 
 # Wildcard target for test code generation:
 # A .c file is generated for each .data file in the suites/ directory. Each .c