Added ABI compatibility tests with native compiler using libtcc.

Only one test so far, which fails on Windows (with MinGW as the native
compiler - I've tested the MinGW output against MSVC and it appears the
two are compatible).

I've also had to modify tcc.h so that tcc_set_lib_path can point to the
directory containing libtcc1.a on Windows to make the libtcc dependent
tests work. I'm not sure this is the right way to fix this problem.

tests/Makefile

@@ -13,6 +13,7 @@ TESTS = \
  hello-run \
  libtest \
  test3 \
+ abitest-exe \
  moretests
 
 # test4 -- problem with -static
@@ -177,6 +178,15 @@ asmtest: asmtest.ref
 	objdump -D asmtest.o > asmtest.out
 	@if diff -u --ignore-matching-lines="file format" asmtest.ref asmtest.out ; then echo "ASM Auto Test OK"; fi
 
+# Check that code generated by libtcc is binary compatible with
+# that generated by CC
+abitest$(EXESUF): abitest.c $(top_builddir)/$(LIBTCC)
+	$(CC) -o $@ $^ $(CPPFLAGS) $(CFLAGS) $(NATIVE_DEFINES) $(LIBS) $(LINK_LIBTCC) $(LDFLAGS) -I$(top_srcdir) -g -O0
+
+abitest-exe: abitest$(EXESUF)
+	@echo ------------ $@ ------------
+	abitest$(EXESUF) lib_path=..
+
 # targets for development
 %.bin: %.c tcc
 	$(TCC) -g -o $@ $<