win32: adjust new unicode support

- lib/Makefile: add (win)crt1_w.o

- crt1.c/_runtmain: return to tcc & only use for UNICODE
  (because it might be not 100% reliable with for example
  wildcards (tcc *.c -run ...)

- tccrun.c/tccpe.c: load -run startup_code only if called
  from tcc_run(). Otherwise main may not be defined.  See
  libtcc_test.c

- tests2/Makefile: pass extra options in FLAGS to allow
  overriding TCC

Also:
- tccpe.c: support weak attribute.  (I first tried to solve
  the problem above by using it but then didn't)

lib/Makefile

@@ -41,7 +41,7 @@ I386_O = libtcc1.o alloca86.o alloca86-bt.o $(BCHECK_O)
 X86_64_O = libtcc1.o alloca86_64.o alloca86_64-bt.o $(BCHECK_O)
 ARM_O = libtcc1.o armeabi.o alloca-arm.o
 ARM64_O = lib-arm64.o
-WIN32_O = crt1.o wincrt1.o dllcrt1.o dllmain.o chkstk.o
+WIN32_O = crt1.o crt1w.o wincrt1.o wincrt1w.o dllcrt1.o dllmain.o chkstk.o
 
 ifeq "$(TARGET)" "i386-win32"
  OBJ = $(addprefix $(DIR)/,$(I386_O) $(WIN32_O))