Fix command spawning on Cygwin-based standalone image.

In the standalone image, we need a /bin/sh interpreter
for the sh and open-command functions to work. The / path
resolves to the installation directory, thanks to some
sysrooting logic in the Cygwin DLL. Thus, we just need
a sh.exe program in the bin directory, side by side
with txr.exe. This sh.exe program can translate the
"sh -c command" invocation to "cmd.exe /c command".

* Makefile (sh.exe): New target, built from cmdwrap.c.

* cmdwrap.c: New file.

* inst.nsi: Install sh.exe.

1 files changed, 17 insertions, 0 deletions

diff --git a/cmdwrap.c b/cmdwrap.c
new file mode 100644
index 00000000..51e44b07
--- /dev/null
+++ b/cmdwrap.c
@@ -0,0 +1,17 @@
+#include <process.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main(int argc, char **argv)
+{
+   if (argc != 3)
+     return EXIT_FAILURE;
+
+   if (strcmp(argv[1], "-c") != 0)
+     return EXIT_FAILURE;
+
+   argv[0] = "c:/Windows/System32/cmd.exe";
+   argv[1] = "/c";
+
+   return spawnvp(_P_WAIT, argv[0], (const char * const *) argv);
+}