add a wrapper for ssh-keygen

Build/NullSoftInstaller.hs

@@ -199,4 +199,7 @@ findCygLibs p = filter iscyg . mapMaybe parse . lines <$> readProcess "ldd" [p]
 	iscyg f = "cyg" `isPrefixOf` f || "lib" `isPrefixOf` f
 
 wrappers :: [FilePath]
-wrappers = ["standalone\\windows\\ssh.cmd"]
+wrappers = 
+	[ "standalone\\windows\\ssh.cmd"
+	, "standalone\\windows\\ssh-keygen.cmd"
+	]

standalone/windows/ssh-keygen.cmd

@@ -0,0 +1,31 @@
+@rem Do not use "echo off" to not affect any child calls.
+
+@rem Enable extensions, the `verify other 2>nul` is a trick from the setlocal help
+@verify other 2>nul
+@setlocal enableDelayedExpansion
+@if errorlevel 1 (
+    @echo Unable to enable delayed expansion. Immediate expansion will be used.
+    @goto fallback
+)
+
+@rem Get the absolute path to the parent directory, which is assumed to be the
+@rem Git installation root.
+@for /F "delims=" %%I in ("%~dp0..") do @set git_install_root=%%~fI
+@set PATH=!git_install_root!\bin;!git_install_root!\mingw\bin;!PATH!
+
+ssh-keygen %*
+@goto end
+
+:fallback
+@rem The above script again with immediate expansion, in case delayed expansion
+@rem is unavailable.
+@for /F "delims=" %%I in ("%~dp0..") do @set git_install_root=%%~fI
+@set PATH=%git_install_root%\bin;%git_install_root%\mingw\bin;%PATH%
+
+@if not exist "%HOME%" @set HOME=%HOMEDRIVE%%HOMEPATH%
+@if not exist "%HOME%" @set HOME=%USERPROFILE%
+
+ssh-keygen %*
+
+:end
+@rem End of script