lib/Makefile: fix out-of-tree build of lib/bt-exe.c

Commit a522213 ("tccpe.c: never assume static...") removed the global
-I$(TOP) for cleaner lib build, and ensured that it is added for
bcheck.c as it now includes config.h, but forgot that bt-exe.c also
needs config.h, as it includes ../tccrun.c which includes it.

Also, the explicit tccrun.c prerequisite for bt-exe.c is not required,
as all *.o lib files depend on $(TCC), which depends on libtcc, which
depends on tccrun.c .

Also, at win32/built-tcc.bat, while bcheck.c needs -I.. for config.h,
bt-exe.c doesn't, as ../tccrun.c does find it where it expects it.

lib/Makefile

@@ -92,7 +92,8 @@ $(TOP)/%.o : %.c $(TCC)
 	$S$(XCC) -c $< -o $@ $(XFLAGS)
 
 $(TOP)/bcheck.o : XFLAGS += $(BFLAGS) -I$(TOP)
-$(TOP)/bt-exe.o : $(TOP)/tccrun.c
+# includes tccrun.c, $(TOP) for config.h  (tccrun.c prerequisite via $(TCC))
+$(TOP)/bt-exe.o : XFLAGS += -I$(TOP)
 
 $(X)crt1w.o : crt1.c
 $(X)wincrt1w.o : wincrt1.c