Make dart_api.h C compatible.

Make dart_api.h C compatible.

BUG=3024
Committed: https://code.google.com/p/dart/source/detail?r=7666

[cshapiro, 2012-05-13 08:16:08]

Tested as follows...

$ cat > test.c
#include <stdio.h>
#include "dart_api.h"
int main() {
  printf("%zd\n", sizeof(struct Dart_CObject));
  return 0;
}
$ clang test.c
$ gcc test.c

[Bill Hesse, 2012-05-14 13:28:09]

This should be fine, but I would be extremely careful about checking that it
does not break any Windows or MacOS C++ compilation.  I would also check on
which platforms it fixes C compilation, and note that in the bug.

Does this fix C compilation on all platforms, including Windows?  I don't think
it has stdbool.h, but I can check.

Do you need help checking it on Windows and MacOS?  I can try it on my machines.

LGTM, if it does not break anything.  A verified complete solution would be
best.

[turnidge, 2012-05-14 17:08:21]

lgtm

[cshapiro, 2012-05-15 18:39:35]

You are correct, Win32 does not have stdbool.h, nor does it have inttypes.h. 
Those includes are somewhat confusingly on the other side of an #else which
ensure a clean compile on Win32.