test: backport use executable in spawn() test

Backport 1070377 from the v0.12 branch.

Currently, the test-child-process-spawn-typeerror.js is
calling execFile() on a JavaScript source file, which is
causing failures on Windows. This commit switches to calling
spawn() on an actual executable.

Fixes nodejs#8930.

Signed-off-by: Julien Gilli <julien.gilli@joyent.com>

Author: cjihrig

test/simple/test-child-process-spawn-typeerror.js

@@ -41,10 +41,10 @@ assert.doesNotThrow(function() { spawn(cmd, a, o); });
 assert.doesNotThrow(function() { spawn(cmd, o); });
 
 // Variants of undefined as explicit 'no argument' at a position
-assert.doesNotThrow(function() { execFile(empty, u, o); });
-assert.doesNotThrow(function() { execFile(empty, a, u); });
-assert.doesNotThrow(function() { execFile(empty, n, o); });
-assert.doesNotThrow(function() { execFile(empty, a, n); });
+assert.doesNotThrow(function() { spawn(cmd, u, o); });
+assert.doesNotThrow(function() { spawn(cmd, a, u); });
+assert.doesNotThrow(function() { spawn(cmd, n, o); });
+assert.doesNotThrow(function() { spawn(cmd, a, n); });
 
 assert.throws(function() { spawn(cmd, s); }, TypeError);
 assert.doesNotThrow(function() { spawn(cmd, a, s); }, TypeError);