add launchdf binary so steam has an exe to launch

CMakeLists.txt

@@ -615,3 +615,5 @@ if(BUILD_SIZECHECK)
     add_subdirectory(depends/sizecheck)
     add_dependencies(dfhack sizecheck)
 endif()
+
+add_subdirectory(package/windows)

package/windows/CMakeLists.txt

@@ -0,0 +1,7 @@
+project(package_windows)
+
+if(WIN32)
+    add_executable(launchdf WIN32 launchdf.c)
+    install(TARGETS launchdf
+        DESTINATION ${DFHACK_DATA_DESTINATION})
+endif()

package/windows/launchdf.c

@@ -0,0 +1,42 @@
+#include <windows.h>
+
+int WINAPI wWinMain(HINSTANCE hi, HINSTANCE hpi, PWSTR cmd, int ns)
+{
+    STARTUPINFOA si;
+    PROCESS_INFORMATION pi;
+
+    ZeroMemory(&si, sizeof(si));
+    si.cb = sizeof(si);
+    ZeroMemory(&pi, sizeof(pi));
+
+    CHAR dfdir[1024];
+
+    if (GetFullPathNameA("..", 1024, dfdir, NULL) == 0)
+    {
+        MessageBoxA(NULL, "could not get current directory", NULL, 0);
+        exit(1);
+    }
+
+    if (SetCurrentDirectoryA(dfdir) == 0)
+    {
+        MessageBoxA(NULL, "could not change to DF directory", NULL, 0);
+        exit(1);
+    }
+
+    if (CreateProcessA("Dwarf Fortress.exe",
+        NULL,
+        NULL,
+        NULL,
+        FALSE,
+        0,
+        NULL,
+        NULL,
+        &si,
+        &pi) == 0)
+    {
+        MessageBoxA(NULL, "could not launch 'Dwarf Fortress.exe'", NULL, 0);
+        exit(1);
+    }
+
+    exit(0);
+}