Replace CRT-free return with ExitProcess (#82)

ConEmu injects a thread (ConEmuCD.dll) and injects a DLL that starts
threads (ConEmuHk.dll). These threads may linger after the main thread
has returned, delaying the process exit and even interfering with the
exit status. As a work around, call ExitProcess instead of returning
from the main thread. This terminates extra threads so that the process
will no longer wait for their voluntarily exit.

src/alias.c

@@ -39,6 +39,8 @@ typedef struct {
 int CreateProcessW(
     void *, void *, void *, void *, int, int, void *, void *, void *, void *
 ) __attribute((dllimport,stdcall));
+void ExitProcess(int)
+    __attribute((dllimport,stdcall));
 char16_t *GetCommandLineW(void)
     __attribute((dllimport,stdcall));
 int GetExitCodeProcess(void *, int *)
@@ -128,11 +130,7 @@ static void fail(char *reason, int len)
     WriteFile(out, reason, len, &dummy, 0);
 }
 
-#if __i386
-__attribute((force_align_arg_pointer))
-#endif
-__attribute((externally_visible))
-int mainCRTStartup(void)
+static int aliasmain(void)
 {
     // Replace alias module with adjacent target
     char16_t exebuf[MAX_PATH];
@@ -179,3 +177,13 @@ int mainCRTStartup(void)
     GetExitCodeProcess(pi.process, &ret);
     return ret;
 }
+
+#if __i386
+__attribute((force_align_arg_pointer))
+#endif
+__attribute((externally_visible))
+int mainCRTStartup(void)
+{
+    int r = aliasmain();
+    ExitProcess(r);
+}

src/debugbreak.c

@@ -73,5 +73,6 @@ mainCRTStartup(void)
             CloseHandle(h);
         }
     }
-    return GetLastError() != ERROR_NO_MORE_FILES;
+    int status = GetLastError() != ERROR_NO_MORE_FILES;
+    ExitProcess(status);
 }

src/w64devkit.c

@@ -152,5 +152,5 @@ mainCRTStartup(void)
     DWORD ret;
     WaitForSingleObject(pi.hProcess, INFINITE);
     GetExitCodeProcess(pi.hProcess, &ret);
-    return ret;
+    ExitProcess(ret);
 }