Add some tests for the amalgamated source/

Adds tests to Makefile and CI on Poisx platforms.

test/amalg/main.c

@@ -0,0 +1,36 @@
+/*
+* Copyright (c) 2019 Calvin Rose
+*
+* Permission is hereby granted, free of charge, to any person obtaining a copy
+* of this software and associated documentation files (the "Software"), to
+* deal in the Software without restriction, including without limitation the
+* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+* sell copies of the Software, and to permit persons to whom the Software is
+* furnished to do so, subject to the following conditions:
+*
+* The above copyright notice and this permission notice shall be included in
+* all copies or substantial portions of the Software.
+*
+* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+* IN THE SOFTWARE.
+*/
+
+/* A simple client for checking if the amalgamated Janet source compiles
+ * correctly. */
+
+#include <janet.h>
+
+int main(int argc, const char *argv[]) {
+    (void) argc;
+    (void) argv;
+    janet_init();
+    JanetTable *env = janet_core_env(NULL);
+    janet_dostring(env, "(print `hello, world!`)", "main", NULL);
+    janet_deinit();
+    return 0;
+}