tests: Added numerous tests.

The tests are taken almost verbatim from the open source project PicoC. It can
be found at https://code.google.com/p/picoc/.

The tests range from very simple/trivial ones to more complicated. My view is
that the more tests the better. Without tests like this I was very reluctant to
make any changes to tcc for the fear of breaking things.

The tests pass on Win32, OSX, Linux x86 and x86_64. One or two tests fail on
each platform due to differences in the runtime library.

tests2/15_recursion.c

@@ -0,0 +1,21 @@
+#include <stdio.h>
+
+int factorial(int i) 
+{
+   if (i < 2)
+      return i;
+   else
+      return i * factorial(i - 1);
+}
+
+int main()
+{
+   int Count;
+
+   for (Count = 1; Count <= 10; Count++)
+      printf("%d\n", factorial(Count));
+
+   return 0;
+}
+
+/* vim: set expandtab ts=4 sw=3 sts=3 tw=80 :*/