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.

tests2/07_function.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+
+int myfunc(int x)
+{
+   return x * x;
+}
+
+void vfunc(int a)
+{
+   printf("a=%d\n", a);
+}
+
+void qfunc()
+{
+   printf("qfunc()\n");
+}
+
+int main()
+{
+   printf("%d\n", myfunc(3));
+   printf("%d\n", myfunc(4));
+
+   vfunc(1234);
+
+   qfunc();
+
+   return 0;
+}
+
+// vim: set expandtab ts=4 sw=3 sts=3 tw=80 :