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)

win32/build-tcc.bat

@@ -137,12 +137,12 @@ copy>nul tiny_libmaker.exe tiny_libmaker-m%T%.exe
 %CC% -o tiny_libmaker-m%TX%.exe tools\tiny_libmaker.c %DX%
 
 :libtcc1.a
-@set O1=libtcc1.o crt1.o wincrt1.o crt1_w.o wincrt1_w.o dllcrt1.o dllmain.o chkstk.o bcheck.o
+@set O1=libtcc1.o crt1.o crt1w.o wincrt1.o wincrt1w.o dllcrt1.o dllmain.o chkstk.o bcheck.o
 .\tcc -m32 %D32% -c ../lib/libtcc1.c
 .\tcc -m32 %D32% -c lib/crt1.c
-.\tcc -m32 %D32% -c lib/crt1.c -D_UNICODE -DUNICODE -o crt1_w.o
+.\tcc -m32 %D32% -c lib/crt1w.c
 .\tcc -m32 %D32% -c lib/wincrt1.c
-.\tcc -m32 %D32% -c lib/wincrt1.c -D_UNICODE -DUNICODE -o wincrt1_w.o
+.\tcc -m32 %D32% -c lib/wincrt1w.c
 .\tcc -m32 %D32% -c lib/dllcrt1.c
 .\tcc -m32 %D32% -c lib/dllmain.c
 .\tcc -m32 %D32% -c lib/chkstk.S
@@ -153,9 +153,9 @@ tiny_libmaker-m32 lib/32/libtcc1.a %O1% alloca86.o alloca86-bt.o
 @if errorlevel 1 goto :the_end
 .\tcc -m64 %D64% -c ../lib/libtcc1.c
 .\tcc -m64 %D64% -c lib/crt1.c
-.\tcc -m64 %D64% -c lib/crt1.c -D_UNICODE -DUNICODE -o crt1_w.o
+.\tcc -m64 %D64% -c lib/crt1w.c
 .\tcc -m64 %D64% -c lib/wincrt1.c
-.\tcc -m64 %D64% -c lib/wincrt1.c -D_UNICODE -DUNICODE -o wincrt1_w.o
+.\tcc -m64 %D64% -c lib/wincrt1w.c
 .\tcc -m64 %D64% -c lib/dllcrt1.c
 .\tcc -m64 %D64% -c lib/dllmain.c
 .\tcc -m64 %D64% -c lib/chkstk.S