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.

tests2/25_quicksort.expect

@@ -0,0 +1,2 @@
+62 83 4 89 36 21 74 37 65 33 96 38 53 16 74 55 
+4 16 21 33 36 37 38 53 55 62 65 74 74 83 89 96