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.

tests2/02_printf.expect

@@ -0,0 +1,15 @@
+Hello world
+Count = -5
+Count = -4
+Count = -3
+Count = -2
+Count = -1
+Count = 0
+Count = 1
+Count = 2
+Count = 3
+Count = 4
+Count = 5
+String 'hello', 'there' is 'hello', 'there'
+Character 'A' is 'A'
+Character 'a' is 'a'