makefile: unify cross with native builds

supports building cross compilers on the fly without need
for configure --enable-cross

   $ make cross          # all compilers
   $ make cross-TARGET   # only TARGET-compiler & its libtcc1.a

with TARGET one from
   i386 x86_64 i386-win32 x86_64-win32 arm arm64 arm-wince c67

Type 'make help' for more information

win32/include/_mingw.h

@@ -83,8 +83,12 @@
 #define _M_IX86 300 /* Visual Studio */
 #define WIN32 1
 #define _USE_32BIT_TIME_T
+#ifdef __arm__
+#define __TRY__
+#else
 #define __TRY__ void __try__(void**), *_sehrec[6]; __try__(_sehrec);
 #endif
+#endif
 
 /* in stddef.h */
 #define _SIZE_T_DEFINED