tests: Take in account Makefiles that have meaning for rebuild only.

Currently, targets dependancy list don't include Makefile.in,
this leads to incomplete rebuild after target's compiler/linker
flags was changed.
Use "$(wildcard)" function due to Makefile.in could be absent
in subdirectory.

Signed-off-by: Leonid Lisovskiy <lly.dev@gmail.com>

test/Test.mak

@@ -116,7 +116,7 @@ compile: $(COMPILE_TARGETS)
 G_TARGET_SRCS := $(addsuffix .c,$(G_TARGETS))
 U_TARGET_SRCS := $(addsuffix .c,$(U_TARGETS))
 
-MAKE_SRCS := Makefile $(TESTDIR)Makefile $(TESTDIR)Rules.mak $(TESTDIR)Test.mak
+MAKE_SRCS := $(wildcard Makefile.in) $(TESTDIR)Makefile $(TESTDIR)Rules.mak $(TESTDIR)Test.mak
 
 $(U_TARGETS): $(U_TARGET_SRCS) $(MAKE_SRCS)
 	$(showlink)