glu: Fix some compiler warnings in libtess

When compiled with the more aggressive compiler warnings such as
-Wshadow and -Wempty-body the libtess code gives a lot more
warnings. This fixes the following issues:

* The 'Swap' macro tries to combine multiple statements into one and
  then consume the trailing semicolon by using if(1){/*...*/}else.
  This gives warnings because the else part ends up with an empty
  statement. It also seems a bit dangerous because if the semicolon
  were missed then it would still be valid syntax but it would just
  ignore the following statement. This patch replaces it with the more
  common idiom do { /*...*/ } while(0).

* 'free' was being used as a local variable name but this shadows the
  global function. This has been renamed to 'free_handle'

* TRUE and FALSE were being unconditionally defined. Although this
  isn't currently a problem it seems better to guard them with #ifndef
  because it's quite common for them to be defined in other headers.

https://bugs.freedesktop.org/show_bug.cgi?id=28845

Signed-off-by: Brian Paul <[email protected]>

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